Your BEST choice would be FreeBSD
FreeBSD is not linux.. but it's another unix-like OS.. famous for it's performance and stability, particularly as a web server.. if you go take a look on netcraft.. all of the top 50 web hosting servers run FreeBSD...
If you are intent on using linux no matter what.. as the previous poster said.. RHEL is good... SuSE is also popular... Slackware is a great choice.. and very rock solid... the choice is yours.. and that's what *nix is about.. the freedom to choose...
Good Luck...