They're basically the same. For me, I'm pretty sold on Visiontek products. I've bought five different Visiontek cards over the course of the last year (one GF2 MX200, two GTS-Vs', one GF3, and one GF4 ti4600). The ti4600 overclocks very well (not that it needs it) and has excellent image quality.
Visiontek's quality is getting better and better. The only thing I don't like about them is that the price is getting higher and higher as well, now that they've become so prominent.