Probably the GBA versions of V and VI as their new scripts and localization make them 100x more epic and enjoyable. FFT: War of the Lions also gained some excellent new translations and some awesome new extra story parts that actually expand some characters and best of all, doesn't feel tacked on. I want to play IV DS before I make a judgment call on this game.

Overall, SE has done a phenomenal job on their ports and puts extra care to make each of them retains their excellent quality.