i use sculpey III cause its the most readily available one, and its cheaper than the FIMO i seen. also, i love that i can buy the 30 pack sampler (ive also seen the FIMO sampler, but i much prefer the sculpey sampler cause the colours are waay better). ive got some grey FIMO, but i dont really use it xD
Mainly Sculpey and this random brand I found at the art store called Kreall-therm or something like that... I prefer Sculpey but Kreall-therm has some neat colours and the store gets more of that than they do sculpey for some reason. I've used some premo-sculpey too but found that a bit too hard.. and I bought white and red Fimo once and it was really rock hard so I don't use Fimo anymore if I can help it..
I generally use fimo soft because it is easier to find where i live and sculpy (any brand) when i can find it. I bought a block of puppen in white (as it was the largest pale colour they had in stock) but it is VERY hard and takes a long time to condition. I dunno if you're supposed to but sometimes i mix fimo and sculpy together to make my own colour blends, haven't had any adverse effects yet.