I use a light pic on lead (more control) and I used to use light pic on rythem too, but now Im trying to use the harder once because u get a better sound and much heavyer sound. On chords I only use my fingers...

I just have to say somethink; ( I read this on guitarworld.com written by Dimebag Darell, pantera) Dimebag wrote that he scrached (is it how its written?) his pic, so that if he got a bit swetty on his fingers it wouldn't slip out of his finger.

I tried it, and it workes great!