I personally prefer AMD....they do more work per cycle and I think they are just better all around chips.
As far as incompatibilities I don't know of any. These guys might know of something, but I don't.
I think you should still stick with Mandrake since you are just getting your feet wet. Once you get past that and feel against their business practices, then go with RH or maybe be cool and use an apt-get system like Debian! ;D