They serve completely different roles.
Xfire is mostly a communicator, a job it does very well. It does have some server browsing ability, but that's fairly limited.
GameRanger solves connection issues and actually helps you play these games online. For Borderlands, in particular, this has been a serious issue.
Thanks, guys. :)
Thanks for the mention. Yeah, Borderlands can already use GameRanger (and in fact, it was popular at the time of release due to the badly functioning GameSpy tech). BF2 looks like it should be possible to add.