If you're just sticking it in your filter, so long as its made specifically for aquariums and filters then just about anything is pretty much the same and should be fine. Personally, I just head over to my local Petsmart and pick up a little box of those white Fluval filter sponge sheets...I think they're about $7 for a pack of two? The pores are large enough, without being too large, to make good baffles too, which is why I like them.
IMO, sponge is a better media then the floss that comes on cartridges and such. On top of some extra space for BB to colonize, sponge isn't going to wear down and fall apart like floss will eventually.