Silicone, for sure, just because of the wide variety of firmness or softness it's available in now days. It offers alot of versatility. I also love other body safe options such as Glass, Wood, and Stainless.
Glass for me. I prefer the hardness of it. And it doesn't collect lint and I never need to use lots of lube with it. I would probably like metal also, but those tend to be more expensive and I haven't saved up for one yet
ATM I buy strictly silicone but that's only because I haven't had the chance to get a glass toy, although I've been REALLY wanting to get a casper. I'd also buy metal (which is really expensive) or non-porous TPR/TPE