it depend render you want
.flac is studio quality and its high weight (best quality)
.ogg is light and good for videogame (medium quality)
personaly i use mp3 22kertz or less for have an oldschool timbre (low quality)
more quality = more weight
so you have to adapte for what you need
(for exemple for a game like guitare hero you should use .flac, for a 8bitgame you can just use mid(ugly) or ogg)