If I'm Cloud, I'll marry both of them.
Ok, I'll tell you about my opinions. Let's see:
Cloud loves Aeris & Tifa. Meanwhile, Tifa & Aeris love Cloud too. And, Aeris and Tifa really get along well.
So, the only thing left for Cloud is to take action (Just marry them already)desperately! Cloud should just forget about Sephiroth and then get married with Tifa & Aeris. I think that Cloud's going after Sephiroth because of the personal feud, it's not about saving the world.... (In the beginning of the story, I mean.) Please don't worry about Sephiroth, I'm sure Barret'd take a good care of him.
It's so simple, I've resolved all the problems!
