I'd go for VII or X. I wouldn't say IX is overrated. A lot of people are big fans of it on EoFF (myself included), as Aaron said, but amongst my offline friends, many don't rate IX very highly at all..

Now don't get me wrong, I think VII is a very good game, but I think that the amount of people who seem to consider it the gold standard of computer gaming are a bit off the mark. I enjoy VII very much, but I think there's a lot of people who seem to rate it too highly. In terms of number of overraters, I'd say VII.

In terms of the amount a game is overrated (i.e. the extent to which people think the game is better than I consider it to be, rather than the number of people who overrated it), I think X hits the mark. Again, I like X, despite it being one of my least favourite entries in the series. In terms of story and characters, I think it's weak. Yet there are a lot of people who I know who seem to consider this one of the best games in the series and I'll never for the life of me understand.