I really don't understand why people use batchPCB.
Because people love and trust Sparkfun, other than that, I have no idea. Unless you have something small (say under 4 sq in) your likely cheaper getting someone else to make it. I use them every now and then when I need a breakout board for -that-fscking-small-weird-footprint-device-I'm-tryingout- usually this means I can get 4 breakout boards in less than 3sq in, there's no point paying someone else (or wasting a panel slot) to make 3sqin of something if I only need one set.
This said, if you make mistakes (knock wood), it's nice to mess up one board then mess up 20.