There's really no way to tell which game has more fans, among the people who have played them all.
Yes, FFVII has more fans overall. That's an obvious conclusion when there has been like, 3x more people that have played it.
By the same token, a ton more people like Pokemon, Mario, or Zelda (in the west) over FF. Can I say conclude Mario > FF from this? Not really, it's not a fair comparison, not to mention claiming the majority isn't saying much...
This is only directed to those who claim FF7 > all due to its popularity, when I'm sure many that claim this probably hate the Wii. Of course, I am aware there are those crazed FF6 fanboys that proclaim... well, you know, lol
... on topic. It's simply an awesome game, for all reasons already named. It's got nearly everything I look for in an JRPG, the only one that matches or tops it (IMO) is Chrono Trigger.