AGU has a larger ported head than the AUM and a cable operated throttle, k03 turbo. AUM is fly by wire and has a k03s turbo (k04 internals, maintains higher boost longer). I -think- it's the AUM that has VVT too.
It's arguable which is better, in my opinion a mixture of the two, AGU with k03s makes a nice combination when mapped properly. I heard somewhere that you can stick the vvt unit onto an AGU too, which is nice. </fast show>
toph.