I love the action of RTCW, but I love the nostalgic feel and goosebumps of MOHAA. I don't play multiplayer often, but with these two, RTCW is very fast and action paced, and MOHAA is very exciting and nerve-wracking (often turning into a sniper fest).
Sorry, just can't pick one. If you had an option to pick both...
Just 'cause of smooth action and prettier graphics. (Also because I can't figure out how to disable head-bobbing in MoH:AA and it was a snap in RTCW. )