There exists nothing as "absolute best". Only things appropiate, or better than others for a specific task.Said that, for aac audio, and iTunes, using quicktime's unconstrained vbr mode at 192 is definitely a good setting. Is Vorbis? It's not clear. The tests that we did were done against iTunes' encoder (which is not the unconstrained one) and vorbis seemed to be partially above iTunes. Also note that this was done in 2005 and the encoders have improved.Also, note that newer tests were done with Nero's AAC encoder, which produced better results on the average, so you probably should take a look at this one too.
both the aac and vorbis encoders have advanced, and they are both great for quility per bitrate.If you want another option thats VERY VERY good and encodes/decodes fast try MusePack(mpc) I am activly trying to get musepack support added to the sansa fuze(sandisk seems willing to add codec support, they added ogg and flac already!!!)
however I saw a listening test before some guy said ogg vorbis is the best....is it?