If you use a lot of older BAIB midi styles, these often sound more "right" with VSC as, I suspect, they were written with that in mind. The balance is often better, and, where the style has strings or pads, I nearly always find that VSC sounds better than any of the others. That's not to say that the sounds are better, they just fit better in the mix. Also, you need to bear in mind that the whole VSC and TTS-1 programmes (with 200-odd instruments) are smaller than the middle C samples on their own in a decent sampled piano like Ivory or the While Grand, so you can't expect miracles.

Another thing to bear in mind is that you can swap these very small GM players (VSC / Forte / TTS1) in a few seconds using the Audio/Midi options dialog box, so you don't have to stick with one.

My 2p

Brian