Final Fantasy franchise, seeing as how the last game came out approximately forever ago. The answer recently came in the latest Dutch issue of Official PlayStation Magazine, which contains a revealing interview with Squeenix's Yoshinori Kitase. According to a fan translation of the interview, Kitase said "Final Fantasy XIII was originally meant to be a PS2 title, but we had to switch systems due to the arrival of the PS3. That cost us about one and a half years and was constantly a case of trial and error."
Considering it took Square Enix roughly "one and a half years" to develop and release Final Fantasy IX, that's a pretty substantial amount of time lost. Hopefully the developer will have an easier time when working on the next current-gen Fantasy.