Reply to S4 or VCI-400?

I've been mixing with my Numark N4 for a year and a half now, and I feel like my ability is outgrowing what that mixer can do. I'm saving up for a new mixer and controller, so which is better, the VCI-400, Traktor Kontrol S4, or something else I'm not believeing of? List some pros and cons, and feel free to bring up some new mixers I'm not believeing of.