It is unclear by "fabrication" whether you mean just making the PCB or making the PCB and populating it with parts.
If it is the former, I have had good service -- friendly and quick -- from OshPark, but it seems to have fallen a little behind on the price curve. Its user interface is very nice and allows you to see the Gerbers it creates from your CAD program.
Other PCB makers also offer to create Gerbers, but some of those places suggest that if you are using Eagle v.7.x that you should make your own Gerbers, which is not hard to do. I am sending off a couple of boards in the next week just to compare two of the lowest cost PCB makers. Another consideration is the price breakpoints related to board size . OshPark goes on the board area, others offer a price for a 5cmX5cm, 10cmX10cm and other fixed sizes. My most recent project was just a little over 5cm X <5cm, so I picked a house that had a 5cmX10cm option.
There are several variables and to pick one as "best" cannot be done. You might get more responses, if you name a few houses you are considering and ask for feedback on them.
John