Jane, because Natalie Portman

So Thor, who's spent literally centuries sharing adventures with his presumed future betrothed in Sif, 'falls in love' with Jane, a mortal he spends a few hours with and really shares no meaningful or emotional exchanges with. Why? Because Natalie Portman.

There's always been in Hollywood this presumption of the desirability of its stars, to the point where they are often represented as inherently irresistible. But this is one of those case that beggars belief.

Jane is a boring, flat character with nothing to offer an immortal as a mate. The only quality she possesses that supposedly makes her of value is 'intelligence', evidence of which is not forthcoming in the movie. So basically, he prefers her because she's hot. And we're to assume she's so hot in his estimation that it overrides a deep and abiding relationship shared with a woman who is objectively very attractive herself.

It's one of the major faults of this movie imo. There's too much presumption we will like and care about Jane because of who plays her, and way too little about the character that's actually likeable or interesting.