I don't know about OBS, but last time I bothered with streaming tech there was also a pretty good free program called ffsplit. It used ffmpeg for encoding, and it wouldn't surprise me if OBS does so as well. These are all just GUIs/shells, they have very little impact on performance considering how much resources the encoding itself takes (they maybe take 1-2% of the overall use).
Just use whichever is more comfortable for you. The only downside of xsplit that I can think of is that you can't disable its preview, but again that's a very minor difference in the big picture. It's all about how you configure the encoder.
Edit: actually this is the first program that works with 64bit WoW right off. That's already amazing compared to everything else I've tried. Looks like there's enough settings/options to make it comparable to the functionality of xsplit, which ffsplit didn't have. Looks pretty damn good
Edited by Thaya, 06 January 2013 - 03:16 PM.