what's wrong with the upright basses? To my ears they sound very good. The best so far. Did you already test them?
Nothing wrong with them at all. It´s just that I like the fretless bass and electric bass most. The upright basses have out of the box quite some attack ("klonk") which is not to everybodies liking but you can adjust them to your taste without any problem. The best thing is that you can balance between mike recording and direct recording. Makes a lot of difference to the sound. This library is VERY convincing and most importantly it has an extremely high "playability factor"