"Where should I send my board to?" comes up quite regularly in conversation. I'm actually not the best person to ask. The reason is that when I have boards made I'm looking at more than just functionality, and my demands are typically pretty unique (much to the frustration of CAM engineers, I'm sure). Also, my boards typically do not push the limits of the technology, so I can't say a whole lot about quality in 2+ layer boards, controlled impedance, very fine pitch pads, super thin traces, etc. Still, my experiences -- please take them as such -- may be of value to some.
We should first distinguish between two types of services: "standard" and "pooling". With a standard service the boards are made for you on a panel dedicated to your design. Regardless of the amount you'd order, there will be a one-off "tooling" cost added that mainly covers the creation of mask sets that are used to produce the panel. (If you re-order the board with no changes, there will typically be no tooling cost.) A pooling service adds your design to a panel shared with other designs so that the tooling cost is also shared and becomes a part of the unit price you're quoted.
Pooling is cheaper if you're ordering a small amount of units. But because it only makes financial sense to the producer if there's a large volume of designs, it is typically only available in a limited set of "stackups" (board thickness, soldermask colour, finish, etc.). Sometimes you'll just need to compromise in order to get that reduced cost. (Note that you should add the tooling cost to the amount charged for the boards when comparing prices.)
Notice that I did not quantify what is "small amount", and you'll see that I won't quote prices either, just deal with those qualitatively. The reason is that it's a moving target with too many variables to be meaningful in the long-term. What I write today may not apply tomorrow when a fab changes their service (for example, a pooling service going ENIG finish as default, or a service now offering free shipping worldwide). My suggestion is that based on what you learn from this article, you should get quotations from a few services and compare them for an actual design with the actual quantity that you need.
Here's a summary of fabs I've manufactured boards with in the past year. (These are all boards that I've designed with PCBmodE, btw)
Eurocircuits, EU, pooling/standard
Beta Layout, EU, pooling/standard
Express Circuits, UK, standard
Cambridge Circuits, UK, standard/local
P+M Services, UK, standard/local
Ragworm, UK, pooling
OSH Park, US, pooling
Hackvana, China, standard
Tinyosshop, China, pool?
Below are my experiences with each.
Eurocircuits is a Belgian company that has fabrication facilities in Hungary and Germany. It appears to me that most of their business comes from their pooling services since they constantly invest in tools to make the process easier, which ends up reducing cost for us. Their ordering process and browser-based "design checker" is great for catching last minute issues and can save time by not needing to wait for an "exception" report from an engineer. Eurocircuits' pooling pricing is one of the best I can find in the EU and their pricing engine is comprehensive and it's very useful to be able to play around with it in order to find a good cost break point. It's definitely worth giving it a go. (They also produce great videos showing their manufacturing process.)
If I wasn't fussy about how my boards look, Eurocircuits would have been at the top of my list of go-to fabs. However, I find that for most of my board I cannot use them. They insist on having their production number added to the board for identification. Some of my instructions are often ignored, and I also found that their response time is painfully slow when things don't go smoothly through their automated system. But let me repeat: most people won't encounter the problems I've had with Eurocircuits and as long as you don't care much about the looks of your board and things go through their automated system, the value is excellent.
Beta Layout (aka PCB-POOL)
A German/Irish company that predominately offers a pooling service. Their ordering system is less robust than that of Eurocircuits, but you do get a similar result, which is an immediate quotation for your board. They currently offer ENIG as default and, in some cases, a free solder paste stencil, which is a neat bonus if your board happens to require it. They accept an impressive amount of file formats which could mean fewer possible exceptions which translates into faster delivery. I have only used Extended Gerber with them, though.
There are two things I like about Beta Layout that make them my current go-to more-than-a-few-pieces manufacturer. Firstly, they allow me to not have silkscreen and soldermask at a reduced cost and still be pooled (this came in handy for the business card and emergency kit). Secondly, their customer service has been phenomenal so far. They call me to clear up problems right away, they are responsive, and they even made 'superhero' for free just so I can see the results in physical form after I pointed out some issues! They genuinely go to lengths to make things work out to my satisfaction, and that's a big plus for me. I'm currently expecting my first board with them that has soldermask and silkscreen to come through, and I do hope it comes out well, so I could continue sending boards their way.
Express Circuits is a high-end UK manufacturer. I've used them in the past, before PCBmodE, and one of their senior engineers has been really helpful in giving me feedback on the Gerbers PCBmodE produced earlier on. Express is not a pooling service, so you're going to see a fairly high tooling cost, and they do have a high minimum order limit. However, you do get quality service and quality boards with any customisation you require. For example, soldermask colour is not a factor in pricing, so you can define any RGB colour and they'll mix it! I made the large wall-mounted circuit art 'lifegame' with Express, and am now waiting on a new design from them, on top of two other designs I haven't mentioned publicly yet. When I need a custom job that requires special attention to detail and that crosses their minimum order amount, Express is where I go. It's a pleasure working with a high-end manufacturer, but it does cost more.
"Local", Cambridge Circuits and P+M Services
I put Cambridge Circuits and P+M in the same "local" category. These are the fabs that are close to where you're based. There are a few good reasons for using a local shop: they tend to be super friendly and informative, which counts for a lot; you can visit the shop and get to see and feel some samples of their work in order to get a good idea of how your board is going to come out; they accommodate customisation; boards can be done quickly -- they are sure to accommodate fast turnaround -- and you can go pick them up to save on the shipping time (and cost); and, it feels good to give business to a local provider. Doesn't it?
The down side, of course, is that it's going to be more expensive than the pooling services or, sometimes, than the larger outfits. That's understandable, though in many practical cases cost isn't the main factor in the decision. Another thing to consider is whether the local fab can accommodate your "production" run. If it cannot, it might be worth doing the prototype runs where you're going to go for production so that there are fewer chances for surprises.
Ragworm is a relatively new pooling service operating in the UK and is a division of the larger Stickleback Manufacturing. They offer a distinct orange soldermask and pretty standard default stackup. They promise to deliver the boards within ten days -- shipping is included in the price -- and their pricing is decent if you're making just a few boards. If you're in the UK it's certainly a service to try.
What bothered me with Ragworm was receiving the boards with their logo in silkscreen randomly slapped on my board! There's no mention of this on the ordering process, though I'm told that one can ask for their logo not to be added (as I did the for 'redditoken' shown below). I found their customer service to be quite good and responsive, and also heard from someone who made their first board through them that they were very helpful in guiding her through the process.
OSH Park is a US-based service that operates a submission system that cleverly optimises designs into panels that are sent to be made by a few select US-based manufacturers. OSH Park boards have an ENIG finish and a distinct purple soldemask. Pricing is simple with free worldwide shipping with a slick ordering process that lets you see the post-processed Gerbers, which is a great as a last opportunity to check for problems. Price-wise OSH Park is very attractive for a low quantity order, typically beating similar services on price alone.
However, in my experience, boards can arrive up to a month from the time I placed an order using the free shipping option (I'm in the UK!) I take that into consideration when ordering board from them, and I rarely need boards quickly. Sometimes I cannot use OSH Park due to the lovely purple soldermask since traces don't show through, which takes away one visual dimension that my boards require. The boards arrive with the fasteners that hold the pieces to the panel still attached, and filing them off can take some time and is a bit messy; other pooling services typically provide boards completely and neatly routed out of the panel. Finally, Laen, who runs OSH Park is very technical and passionate about his work and providing quality service, and so when I want custom work within his constraints he accommodates and is open for exploring new ideas. This is great resource for experimenting cheaply.
Chinese manufacturers, Tinyosshop and Hackvana
I've used Hackvana and Tinyosshop for small trial runs with the Chinese manufacturers they work with. In both cases, unfortunately, the boards were not to the standard I expected. Personally, I'd rather pay a bit more and have a direct relationship with the manufacturer and avoid surprises when boards come back. Keeping it close to home and not dealing with language barriers has its advantages. For these reasons I no longer even consider Far East manufacturers. This may changes until I can justify getting a top tier manufacturer. These are very anecdotal experiences and personal preferences, I admit, and I accept that one can get great (and cheap) boards from Chinese manufacturers if one cares to experiment.
As you see, there are quite a few factors to consider when choosing a fab house, and there are many more that I did not even mention! My final recommendation is to try out a few fabs when there's an opportunity in order to test their ordering system, support, and, of course, quality. Every fab will have its quirks, which you only discover when running boards through them for a while and decide whether you can "live" with them or not. There's no short-cut to a fruitful relationship, and this is no exception.
(Please add your thoughts and experiences in the comments!)