all games are not created equal

In all fairness to Guild Wars, I do not think you can compare without talking about the overall cost of playing.  Guild Wars is free after initial purchase which makes a far better value than most, if not all other MMO's. 

Beyond that, Final Fantasy Online failed to meet my expectations for what a FF game should be.  While it had the major classes I was looking for, ie dragoon, summoner, mage, and the such; it did not have a quality gameplay layout.  It often felt hallow, as though only a handful of people were playing. 

Guild Wars on the other hand was exciting.  The classes were a bit strange but once you got the hang of it you could build a character exactly how you wanted.  There was not as much waiting around.  Guild Wars was particularly good at making the game exciting both while soloing and partying.  It effectively made skill and strategy the primary goal, eliminating long grinds for little XP. 

Lastly, in order for an MMO to stand over time it must have decent graphics.  I am personally not into graphics much at all, that is until I fire up Final Fantasy Online.  The fact is that the game looks grainy and slow from the very begining.  The evironments lack any sort of vibrance.  Guild Wars however does not.  The details are not missed in GW. 

Overall GW is just a better game all around.  Cost, Gameplay, Strategy, and Graphics make it a far more entertaining game to play.  Being free, also keeps the numbers relatively high.  It's no WoW but it certainly will curb that craving for MMO action.