Bioshotbb.com
Most accurate bbs I've used out of KSC .25s, TSD .25s, TSD .26s, Goldenball .2s, Goldenball .25s, BB King .25 bios, and G&G .25s.
Sometimes they have feeding issues with midcaps though. Mine feed fairly well (not perfect, but not terrible), but others cannot get them to feed in their mids.
My next choice of bbs would be G&G or BB King. BB King bbs have a lawsuit against their name, by B.B. King's (musician) lawyers (lol seriously?) so they might not be available soon. Their quality has supposedly gone down as well. G&Gs are pretty solid though.