Can't wait for FF15! I liked 13 for what it was (haven't played 14) but this looks like a decent return to form for the series. My favourites are 6 and 9- can never decide between them, both have great stories with an awesome cast of characters- and I really like 12 and 5 as well.
Think the only one I'm not too fond of was 8; it looked amazing (for the time, those cut scenes!) and has epic music, but the story went downhill pretty quickly after a promising start and the characters were a bit bland for me. Oh, and that Crystal Chronicles game on the GC was one of the most boring games I've ever played, didn't even complete it.
But yeah, roll on September! This year's shaping up to be an awesome one for games. :D