JS frameworks are so much alike, anyway. If you've been working with mootools for some time, stick to it. Knowing your framework is much more important than choosing one because of this or that.
In my opinion, mootools is better for advanced javascript programmers, while jquery is better for non-javascript programmers. That's what I think after reading both documentations, mind you, I didn't use any of them. jQuery lacks support for the core of javascript, function binding, object cloning, thread stacking, to name a few.
