Any series could be bigger with better marketing really. What you should be asking is what series you'd want to see marketed better.
So I'll answer what im currently playing is metro:last light
Bet with gooch_destroyer, he wins if FFX and FFX-2 will be at $40 each for the vita. I win if it dont
Sign up if you want to see God Eater 2 get localized!! https://www.change.org/petitions/shift-inc-bring-god-eater-2-to-north-america-2#share