Alright, this thread is old, but I just had to comment;
I really don't think you can compare these two pairings, and there is no "one is better than the other" because the difference between them is just too big.
Ed and Winry: young teenagers, just starting to realise their feelings for each other.
Roy and Riza: grown up adults, with a lot more life experience and confidence.
I love both pairings to death, but voted EdWin, simply because I predicted that Royai would win by a long shot on this forum (Royai seems way more popular than EdWin on here, however in general, I think the pairings are equally popular...? At least that's what I would like to think
Royai has no haters at all, and yet it's supposedly more popular than the both hated and loved EdWin? I don't know, it just doesn't seem fair at all, so please tell me I'm wrong about that xD