None. Not a single one. Which is weird. I mean, romance is not exactly a large part of the experience for me, but usually I can come up with at least ONE pairing I like more than the others, especially in a canon with as large a cast as Harry Potter. But there isn't.
There's a few pairings I hate enough to eclipse the sun, but everything else just gets a 'meh'. Harry/Ginny, the actual canon pairing, feels about as valid to me as Snape getting sucked off by the Sorting Hat.
When I think about it, I think the problem is that Rowling isn't a very good romance writer. Although she includes it all over the place in her works, there's a near-total lack of actual chemistry between the characters, and the end result is just sort of...bland.