Mix is definitely the best for me, because I unlocked 60 Three Stars from the Monster Arena (I think you get them for capturing every monster on Gagazet, not sure though), and two of them gives you Sunburst/Supernova, which by the end of the game was the best overdrive for me (excluding aeon overdrives). I also liked Grand Summon, it really helps during tough bosses. Banishing Blade had awesome effects, although I could never get the button combo in time. Ronso Rages are cool too.