I'm a little confused, but I'd like to keep my music in .mp3 format. .mp4/.aac is kinda superfluous given it only provides minuscule audio improvement for the same bitrate. Look at how badly .ogg failed, too.
It's better to keep the standard because most people already have their collection in mp3, and nobody wants a collection with mixed file formats. If you want better audio, FLAC is definitely the way to go though.
V0 VBR mp3 seems to be the standard nowadays and gives excellent sound quality for the storage size. It is the best format, IMHO.