Which PCB Fabrication / Manufacturer do you use?

I use Seeed and OSHPark

Seeed

Was the cost affordable? Yes, both production and shipping costs for 2 and 4 layer boards are competitive

How was the quality? 3 out of my 4 orders were of high quality. One order, obviously made by a different facility, was below par for alignment, mask did not fully match the layout

Did you change from one manufacturer to another for any reason? Yes, I first check OSH Park. If I need more than 3 PCBs, I usually use Seeed

Did they give you any feedback on your design? Yes, via email, when they spotted errors with the board outline.

How fast did they provide them? 3 weeks, shipping to Europe included

OSHPark

Was the cost affordable? Yes, for their standard offerings. Once your design is out of these specifications (size, layers, finish, amount), the options tend to be more expensive

How was the quality? Always very good

Did you change from one manufacturer to another for any reason? OSHPark is my first option. See question 1 for reasons to order elsewhere

Did they give you any feedback on your design? Automated feedback during upload

How fast did they provide them? 2 weeks, shipping to Europe included

Indeed there are a lot of different vendors out there and for prototyping purposes they all appear pretty good and I find myself choosing based on delivery cost and speed of delivery.

Personally, I like https://oshpark.com/ but then found my postal service charging me additional fees for larger orders as I'm in the EU and they are in the US.

Then there's https://aisler.net/ who are EU based seem to be continually improving with their service offering. Liking them more and more.

Then of course there's JLPCB, PCBWay, Seeed and Elecrow who all provide good service but sometime delivery gets in the way.

I have only used JLCPCB, to make 2-layer, 4-layer and very recently a 1-layer ALU pcb to use for an enclosure panel.  The prices are excellent, especially for boards that are up to 100mm square, even 4-layer.  So far, I've had around 10 different designs created and quality has always been very good.  They are based in China so shipping depends upon options used.  If I used a courier such as Fedex or DHL I've had turn around to my door in the UK in under a week!  This tends to be expensive: say, circa £30 shipping for £2 PCBs.  Regular postage takes around 3 weeks turn around to my door and is cheap.  JLCPCB will collect any taxes or fees at point of order so you don't need to pay the courier's processing fee on top.

My last order with them was for the ALU panel.  The design had no solder mask on the back side so the Gerber for this was 'empty'.  This caused problems with their auto-processing because it doesn't seem able to deal with that perfectly valid situation.  I was contacted by them within 24 hours to explain my options and ask me what I wanted to do, including "fixing" and re-uploading.  I just told them to cover the back side with solder mask and let them get on with it and there were no problems.

For 2-layer boards <= 100mm square I don't think the price and quality can be beaten.  I'd wholly recommend them.

I have used JLCPCB since I started banging out my own boards. The order process is simple. I have found a reason to shop around for a different price point. My board orders are usually never greater than ten. The invoice is in US dollars and doesn't include any additional charges. In my case, customs brokers for Canada have their hand out for an additional $20 per order. For that reason, I usually have a number of different boards combined in one order.

Similar experience here, super-happy with the speed with them - my last order, via FedEx, from date of ordering (on a Saturday), to receiving it in the post, was just under 9 days, and cost me $26.72 (all-inclusive, including shipping) for two different PCBs, in a qty of ten and five. These boards were HASL, 2-layer, smaller than 100x100mm, in black and blue solder mask. 

I use OSHPark for smaller boards and initial runs. For very small boards they can be very cheap as they charge by the square inch. They have the highest quality of any prototyping service I’ve used. For larger quantities and larger boards I usually use Seeed or more recently JLCPCB for cost reasons. They have good quality and have always met the specifications they list on their sites.  Seeed was good in the past about getting back to me if they see a potential problem or have a question before starting fabrication. 

In recent years I have used SEEED, ITEAD STUDIO  and PCBWAY. All provide excellent PCBs at low cost. I didn't use SEEED much due to higher costs. I used ITEAD STUDIO ($1/PCB) before the shipping costs from China skyrocketed from $3 to $25. ITEAD STUDIO has now stopped their PCB service. I now use PCBWAY  - their PCBs are much cheaper ($0.50/PCB) and they arrive faster. They usually ship about 24 hours after the order is accepted. Total time from ordering to receiving PCBs is 5-7 days for courier orders. 

I have been using BasicPCB (here in the USA) for the past 4-5 years.  They have two levels of service, ValueSpec and BasicSpec.  ValueSpec (which I use for one off designs or prototypes) is a low cost option where they choose some of the board specification (thickness, material, finish, color, etc.).  My most recent order used this option on a tiny board (0.66" x 1.3"), the cost was $7.00 for 5 boards.  There BasicSpec (which I use for my customers and when I need to fully spec my PCBs) option allows you to specify thickness, material, finish, color, etc. would have cost $34.00 for the same 5 boards.  With either service the shipping (USPS) is included in the price.  They only offer 2-layer boards.

I've used JLCPCB as they appear to be the best cost effective alternative. PCBNew offers better capabilities and still at an affordable price, but they are more expensive. I recently talked to some guy from PCBNew and they may offer me free or highly discounted fabrication, but I still haven't given them a try yet.

If I could make a suggestion, I would love to see a design challenge or competition that includes PCB fab. I suspect it wouldn't be that difficult to talk to some of these PCB fabs and get them to sponsor the PCB fab part (I've see PCBNew sponsoring many personal PCB projects). This would also give the companies quite a bit of visibility too. 

That would be an interesting design challenge. PCBWAY does a lot of sponsorship as well. Including marketing/selling the PCBs for you if you want.

It would be really great if the contest resulted in element14 "branded" PCBs that could be handed out as "free" give-away items. At $0.50 each they would cost less than most freebies, and they could actually be useful.