I prefer the metal minis but for converting the plastic ones are better. I have collected quite a few over the years. I have collected quite a few of the Star Wars Minis just because they are the only minis of that genre in the 28mm range.

I got a few of the D&D minis but i hate the collectable nature of them. I would buy the individual ones if they are not too pricey. But i am not going to pay more than a few dollars for any prepainted minis.

Reaper is coming out with prepainted minis that are not collectable which means you can buy what ever ones you want with out buying a booster and getting a random assortment. Thus you can order what you need.