I'm a former FFXI and FFXIV player. Thanks to the WoW Forever beta I've been able to play WoW pretty regularly, and I have to say that, even though WoW is a great game, FFXIV is on a whole other level. Leaving graphics aside for obvious reasons (the deliberate choice to stay faithful to the original style), here's what I think:
1) WoW has basically no cutscenes, while FFXIV offers a completely different level of immersion;
2) FFXIV's job system is way more varied and extensive than WoW's (and if we throw FFXI into the mix, you could get lost in it);
3) FFXIV fights are full of mechanics designed to keep every role in the party engaged. There are DPS checks, heal checks, tank checks, etc.;
4) FFXIV fights have a huge positional component. Almost every boss ability can be dodged by moving your character to the right spot at the right time. There are also tons of mechanics where you have to run to one spot or another during the fight.
Obviously there are plenty of downsides too, like the complete lack of a structured economy like WoW's, but yeah.
I'd love to hear from players more experienced with WoW than me: what are WoW's strengths compared to FFXIV?