While I don't use it, Suse 9.3 is mighty good. Arch, Crux, Debian, Gentoo, and Slackware are my favorites (not in that order), though.
If it were me, I'd keep my WinXP around for a little while longer (just for comfort), and then my favorite (at the time) Linux distro. Since you are comfortable with triple booting, I'd use the other partitions to experiement with other Linux distros, replacing my old favorite with any new favorite as it might come along. Playing with distros is a bit of a hobby for me.