Fedora is more of a bleeding-edge (or at least developer-focused) distro - they also ship with Ruby 1.9 instead of 1.8.
+1 for Fedora :)
Arch Linux all the way!
Interesting, until last year I used to use Ubuntu when I wanted a bleeding edge and lightweight OS for, say, working with new hardware. How things change.
Fedora has always been bleeding edge. In my experience, to the point of being unstable, at least when a version is new (Installed Fedora 15 the day it came out, segfaults galore).
In its lifetime Ubuntu has never been bleeding edge nor lightweight compared to many other distros. I'm an Arch user all the way but I still take other distros for a test drive every so often and it amazes me the crap distros bundle together in packages when so many things could be made to be optional dependencies. I guess it all depends on your standard for lightweight :).
Fedora is certainly more bleeding-edge. Ruby 1.8 end of life is June 2013 however. It is unfortunate that most distros still ship with 1.8.7 as the default.