Ultimate X-Men is a reboot that tries to bring the superheroes more into "reality", but it's crap anyway. Astonishing is a tiny bit better, but it's some other crap. Xtreme X-Men is better.
The X-Men franchise has been destroyed over the last 10 years or so. Marvel tried to capitalize too much by launching a shitload of titles, not to say awfully written by guys like Mike Carey. So, I still stick to the good ol' Chris Claremont times (but PLEASE don't read X-Men Forever, it sucks)