Hmm. If I had to say, I'd probably go with Final Fantasy.
Not that I didn't like the series, I thought it was fun (yes even XIII).
The only FF games I didn't exactly like was FFXI and, most likely, FFXIV.
While Final Fantasy was, or is depending on your viewpoint, a good series;
It has gone on for quite a while. It's like a person who doesn't stop when they start moving,
Square Enix gained good money from the FF franchise and as such, they're mostly content to
keep making games of/for it, and a good number of people are content to continue buying the games
(I believe so, at least)
So yeah. FF went good, but it's like that one saying 'too much of a good thing can be/get bad'.
At least FF also tried different genres within itself, but I still stand by my main point.