If I made a list of my favorite FF heroes and heroines, I think both lists would consist entirely of characters from FFVI and FFXII (and I've played all the games in the numbered series, minus XI).
As for the 25th Anniversary PSN sale, I am considering getting V and VI. I recall hearing that VI is a port of the PSX version of the game, which I heard was terrible. I already own the SNES cart, so that purchase would be fluff. I haven't heard anything about the port of V and whether or not it is decent or not. I sort of feel like I should buy it out of principal, since I played it on that which shall not be named over a decade ago. Not to mention I've never beaten it, and I've beaten just about all the other numbered FFs.