To be honest I don't take relationships in FF VII too seriously, and see them more as sweet fun, or personal enjoyment. I like Cid x Vincent, but the main reason why is a bit silly and it would never hold up in something like a debate.
It's more for entertainment, and honestly could care less if they ended up canon or the pairing is total crack xD
I love Aeris x Tifa, Cid x Vincent, Zack x Aerith and Cloud x Zack. There's a few Cloud x Sephiroth fanarts that look sexy, but that's about it. Cloud has a burning utter hate for Sephiroth, so that crack pairing don't make too sense, plus most of the fanarts look like rape.
Aeris x Tifa make a wonderful ship, because they seem like more than just friends, they have a wonderful and spiritual connection, and it's stupid when fans act like they were bitter rivals over one spiky haired young adult's attention. No, they understood each other pretty well, and Tifa is the only one that senses Aerith's presence on the Shera airship in AC. Plus the fanart of them together look sexy and damn fine <3
Cloud x Zack also make a really good potential pair. Zack really is the only one that opened up to Cloud and was really the only friend expect Tifa that he really had. Zack and Cloud, like Aeris and Tifa just have this special bond together that makes them click. Also it's sweet how Zack puts his own life on the line to save Cloud's. Zack is so kindhearted and young Cloud is such a cute moe. <3
Zerith, nothing much needs to be said, they are pretty much canon, and Crisis Core shows us what a innocent, sweet and passionate romantic they had together <3 Plus the 23 wishes thing ! So adorable ! :3