I've tried a whole range of them myself.. started off super small, but ended up with a medium sized one. I think my preference mainly comes down to finding the right fit for me. As far as firmness, I started off with ones that were described as being more "soft" but what I found, is that they have trouble snapping back, after I put them in.. so I use an extra firm one now.. seems to snap back quickly, so I'm not fussing about with the fit.