It depends on the tire.

I've had best results with the following:

Hutch Spiders -- 45f, 48r, best all-around performance on- and off-road. 26x2.0
Intense Micro Knobby -- 60/60. 26x2.25
WTB NanoRaptor -- 60/60. 26x2.1.
Hutch UST Scorpions -- 50/50. 26x2.0