I chose tie. Tony is charming because he is the dick with a heart of gold. Thor is charming in the chivalric sense. Both characters are humorous, but for Tony it boils down to sarcasm and wit. For Thor, his humor comes from being placed in odd situations that he does not understand: Thor goes through a lot of culture shock, which is fun to watch.
As for actor portrayals, as much as I loved Hemsworth's take on the mighty Asgardian, Downey Jr. takes it. It is as if RDJR was born to play Tony Stark. In fact, many people on these forums noted that it was like watching RDJR play a fantasy version of himself, which I feel lends itself to believing him in the role. Hemsworth rocked the screen though. Make no mistake about it.