I've used ext3, reiser, and JFS under Gentoo so far. I'd say just from the "me" benchmark, that Reiser and JFS both outperform ext3 soundly, but noticeable difference between the two (Reiser/JFS), in my usage, is very similar.
Of course, I'm probably not dealing with the same average file size that a web service would, so in that case, Reiser might be the best bet (small file performance).
On a somewhat tangent note: I have noticed that Reiser can run fsck much faster than JFS, so if you need to hard-reboot, that'll shave off some seconds 🙂