How did I not see this thread earlier? Just gonna post now to say XIII is definitely #1, everything else I'm not certain about. Especially if that makes the other two sequels and one of those sequels is a handheld game. I'm not really big on handheld so yeah.
Reading these threads always makes me really grateful for my inability to dislike a game as much as other people seem to. I get so much more enjoyment out of my gaming than they do, which can only be a good thing for me.
Still, it's fun to read bits and bobs (I've had to skimread as I'm far behind and don't know/haven't played most of the games). Crisis Core is the only one that I've played more than a few minutes of and I can see the reasoning but it just doesn't bother me so much. Genesis was meh, but the game itself was enjoyable for me, especially at the end (well, enjoyable might be the wrong word... good, definitely, but sad).