Stop motion looks cool on creatures such as undead skeletons or mechanical creations such as the terminator, but other than that I think stop-motion blows. The "guy in the suit" or animatronics/puppets on the other hand can look very cool if they sport enough detail to suspend disbelief. The big plus for cgi is it's flexibility and that's why George Lucas prefers it whenever possible, imho. In the end that's all he is about - no boundaries for the person trying to tell a story.