They're obviously different, for sure. SSL sounds punchy, while V-S sounds fat. I can only tell you that they sounds really good.
I can mix with just both collection and they compensate each other quite nicely. Of course, more flavours are welcomed, but they're pretty much covered what I want. I'm happy to have both, cause I rarely deal with analog gear and I did a lot of ITB thing. However, V-S can be disturbing when the source track has been captured nicely, SSL will be better for clean boost/cut.
If you're curious, buy an ilok if you don't already have, and download them to give a shot for 7 days demo.
