There's a lot more to consider than what the best file format is:
What hardware is this music being played on/through etc ?
Is this for iTunes playback, or is this for portable usage, such as on your iPod/or other Mp3 player ?
Will you be using an DAC and/or amplifier in the signal chain ?
Are there headphones involved, and if so.. what kind of headphones, and will they be amped, or not amped ?
Because if you're simply playing music back on something like an iMac or a MBP, and you're using some cheap-o speakers connected with a simple line out jack and chord.. then to be honest, it really doesn't matter if you use Mp3, Ogg, or AAC.
If you already have a boat load of files in one particular format, then don't bother changing to something else just for the sake of changing.... Believe me, it's a total waste of time. At that point, no particular format is superior, so long as you're not encoding to anything less than say.. 192kbps. Sure, you can go lower than that, and you likely won't be able to tell the difference on sub par equipment, but the point is that you will one day have better hardware, and at that point, those files will come in handy.
Doug