Get the one with the lifetime warranty. If they both have it, get all new.
If you do it yourself please note you'll need to undo the y-pipe, remove the passenger side wheel & unhook the passenger side tie rod. If you're ok with that, get about 40" of socket extensions, one with a wobble on the end, and a 13mm socket. You can access the top alternator bolt through the driver side wheel well.
PITA, yes, but just think about the $200 you'll save.
