Just to echo previous poster's sentiments, I really enjoyed the Zidane/Garnet romance. I also really wanted Terra and Locke to hook up in Final Fantasy VI, but even as a platonic friendship, that worked.

Personally, though, the most believable romance to me was Squall/Rinoa. It was a very strange and downright stupid dynamic at times, but it was probably the closest thing to 'love' that I've seen in these games. Squall's transition from jerkass to desperate lover was pretty darn accurate in my books, and for all of the strange dialogue, I felt a real (if not strange) sense of infatuation presented between the two. I kind of liked that it wasn't completely straight forward, and that a lot of it was marred by Squall's general awkwardness.

Just in general, I give props to Final Fantasy VIII for pulling off a very 'different' type of love story.