Which one is better.. to me it looks like the aircharger (63 Series) gets more horsepower but the 77 just looks better.. is this all the difference is?

Just read that the 63 series is not legal in some states? Is it too loud or something.. I am looking for a nice rumble but not something that is gonna be loud during normal driving conditions.. thanks ofr any input..

I got the aircharger... works nice for me... a little loud but my music is usually louder =o)