TAKE THAT BACK!!
FFXIII is a hideously flawed game, too much grinding, unneeded level caps, terribly flawed and exploitable battle/stagger system and way too mashy until you get a good while into the game where strategy actually matters.
Don't get me wrong though, I actually love FFXIII but I would never say it was better than LR though, that game is mechanically solid and really customisable and unlike XIII you can't just exploit the mnechanics AKA there's no launch stagger locks in LR where there is in XIII
I've played every Final Fantasy game and honestly, FFXIII wasn't that bad. I liked it actually, but Lightning Returns was by far the best. I enjoyed taking part in the launch event where you had to post screenshots to unlock new costumes.
FFXIII is mostly a guilty pleasure for me, despite all it's hideous flaws I love that game more than I should (in my top 5 FF games XIII-1 is atleast no.4)