I have used SuSE extensively, mandrake and debian quite a bit, and RedHat a little.
I find Mandrake is more likely to partially support something in a buggy fashion, whereas SuSE is mre likely to hold off on releasing something until it is at least reliable enough that a user need not be a linux guru to work with it.
I've used debian and redhat as servers, and I prefer debian as a server distro.