Laughing Banana
Weeping Pickle
This game is so heavily favored to magic users, and there's a complete shortage of viable magic users in this game. Plus the fact that luck hurts the cap of both magic/str so it hurts ignis there (one your normal attacks hit for less compounded by the fact that ignis hits less due to the other cap being weaker).
Luck does hurt strength/magic, yes, but the hit is so low (minus 1 to both of them to maximum cap) when compared when you pick magic/strength as flaw (minus 3 both), you'd better pick Luck as flaw instead. And that minus 1 stat is even more insignificant due to the availability of legendary weapons and more importantly, forging.
Really, it is generally agreed that all in all, Speed/Luck is the best asset/flaw combo, especially in harder difficulties like Lunatic or Lunatic+. Well, of course feel free to pick whatever though if you want, hahaha.