pH is a tough one for test kits. Why not just use a pH monitor or controller? Theres a used one for sale used right now:
http://www.canreef.com/vbulletin/sho...hlight=monitor
There are things I dont like about all of the test kits available to hobbyists. I've yet to see a study done that compares them for accuracy against lab grade testing solutions/equipment so I dont think there is a 'best'.