MOHAA AI seems to be more tactical.  RTCW for me, although i havnt played much RTCW, seems to be rush, rush, hide, hideish..  I think MOH has the more realistic AI outta the two, however, RTCW may be harder.. 
But like i said, i havnt played much RTCW, so dont take my little rant here too seriously  
 
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~Blaze