My top three are Twixie, Rarijack, and Scratchtavia.
 
I like Twixie because Trixie and Twilight are my favorite ponies, I lkie seeing an initial dislike grow into like, then friendship, and then love. I think the path that the relationship takes is very interesting.
 
I like Rarijack because I think the ‘opposites attract’ thing can actually gain some footing since they have more in common than they think.
 
I like Scratchtavia because, as I said for Rarijack, I like it when a pair has an obvious reason why they wouldn’t be romantically involved, but there are qualites between them that lead to more personal feelings.