One thing to keep in mind is that if you go with a fully rigid frame, you need to get one with a suspension corrected fork (a la the Surly 1x1) or you can't throw on a sus fork without jacking up your angles.

Me, I like the rigid because I like the firm positive feedback and handling. On the other hand, I'm probably not as serious a mountain biker as many others. I do believe that it helps you with your handling. You become more adept and finding your line, the right timing, all of that sort of thing.