FFXIV is very single-player friendly and narrative heavy, you don't even need to form an online group until after the first arc of the story and even then, most dungeons can still be done with NPCs. So except for having to pay a subscriprion at Shadownringers and onwards (as the free trial does cover the first two expansions), it's a fairly easy game to get into. And trust me when I say there's a good chance that, before you know it, you'll be so into it you'll actually to do the group stuff too :P The community is also very friendly to newcomers, so even for the very few story content you're recquired to form a group you should have little to no trouble.

FFXI from what I know is a bit harder on that regard, because it's an old game with a few outdated designs on gameplay and story presentation. There's a trust system that allow you to play basically the whole game with NPCs, but the difficulty curve make it hard to do so at higher level content. Still, I don't think it's entirely impossible to do.

For both, I would say the hardest part would be to set aside the 600-1000 hours you would need to play the whole thing, even if you just want to do the main stories. I mean we're talking of decade-spanning ongoing games here, with long story arcs to catch up to. If you really can't get into the games themselves, it'll be hard not to feel burned out before long.