From personal encoding experience, seems to me LAME mp3 is close to ogg in terms of size and quality (for 16bit sound anyway). I uploaded some sample tracks of different encoding of the same wave file so anyone can see for themselves. (I would encode from .raw data but do not have the technology in my hands to do so.) Nero He - AAC v2 m4a basically outclasses everything else out there - based on tests run months ago. The m4a is 44kbps, rest are standard 128kbps. I can tell the difference, but most can't, and if you plan on using m4a in the first place then there is no "difference", you just use 1/4 the size for your sounds.
Reason there isn't 24bit and 32bit mp3 or ogg is because it turns into loud static when encoding with those settings. Note some hardware might not support 24 & 32bit.
I have hundreds of instruments and sounds and I want to compose sounds together at runtime and vary things on a whim to make things more lively. Having 1/4 the size for audio without it sounding like its 1/4 the size would be nice. Even if I'd have to scratch the composing, I'd still like 1/4 the size per song. Might be something to consider looking into.