I bought a Vinci for my son this past summer. It's a good gun and he loves it. The only reason that I was able to afford it was I got an out of this world deal on it and couldn't pass it up. With that being said, of the two guns that you mentioned, I would pick the SX3. I'm pretty sure that it will be the next gun that I get. I have read everything I can get my hands on about this gun and can find very little bad things being said about it. Check it out for yourself and if you can get your hands on both of them, do it, and see which one feels the best. SX3 is reasonably priced as well.
I am second