I'll follow along and rate the Final Fantasy series, including the spinoffs and sequels I've played.
1. Final Fantasy IX (My favourite game in general)
2. Final Fantasy VI (Still one of the best games of all time)
3. Final Fantasy X (The reason I bought a PS2 in the first place. Replayed it just a year ago)
4. Final Fantasy VIII (I like this one much more than what seems to be the general consensus)
5. Final Fantasy XII (I found myself liking this one much more than before when I played it for the second time)
6. Final Fantasy VII (The most overrated game in the series, still great though)
7. Final Fantasy XIII, XIII-2, Lightning Returns(This might be cheating, but I generally group these together as one anyway. They are better than people give them credit for.
8.Crisis Core (Suffers a bit from the randomness of the gameplay, but otherwise really good)
9. Final Fantasy IV (The second most overrated game in the series. Brought actual character development and deeper plotlines to the series, VI just did everything better. Still good)
10. Dirge of Cerberus (Another game I liked much more than a lot of other people, rough around the edges, but I liked the story and focus on Vincent's character)
11. Final Fantasy X-2 (One of the best battle systems in the whole series and the job system was excellent, shame about the story and characters)
12. Final Fantasy III (The job system was fun, other games just improved upon it later)
13. Final Fantasy (A fun little romp even today, but doesn't really measure up to most of the more recent games in the series)
Haven't played II at all, and not enough Tactics or V to rate them. I also need to play Type-O at some point.
This was more difficult to rank than I expected.