Hi...i am a new user here. In my case i tried ITead and PCBWay. The quality of the 4 layer boards is, I think, markedly better than the 2 layer boards when compared at the limit. The drill accuracy is better - they tend to hit closer to the center of the via pad. The solder mask aperture positioning seems to be better as well. When I received my Nanocounter boards back from PCBWay I was very pleasantly suprised to see that the soldermask was intact between the pins on the 0.5mm pitch QFN40 package on every board in the package.