I had the 60mm PSX kit on my VTS and I was happy

Ok, Spax isn't the best make but it was very reasonably priced and considering I only used the car going to and from work, it was fine. If I spent a bit of time on track, then I would have paid the little extra and got a better kit.
As for VSX/PSX kit. The difference is that with my old kit (PSX), you could adjust the smoothness of the ride. I don't think you can do that on the VSX kit.
It really depends on what you use the car for and your budget. Were you going for a 40mm or 60mm kit?