it mostly depends on the beat. I rarely quantize but if I do it's on the hats. most of my snare and kick samples incorporate accents and mimic the use of ghost notes so quantization would ruin that. sometimes I'll go in and adjust the midi notes by hand if something is a bit off. I've been messing around with the MPC groove templates in ableton recently, and I've been having good results with the random timing turned up to around 75%.