I have never tried meth but I gather from a lot of reading (and from what people say in this thread), that it is the most powerful if you are looking to get high off amphetamines.
Even though you say there is more to ADHD than having trouble paying attention, it is clear that you want amphetamines solely for their abuse potential. If you want to keep any chance of having an adderall or dexedrine prescription for a long time, don't abuse the stuff so badly. Drug abuse contraindicates prescription of dexamphetamines, which means as soon as your doctor realises your attitude towards them, you will be switched off them very quickly, and you wont be getting prescribed them again any time soon. If you truly do have ADHD, you are risking worse problems with it by using huge amounts of your medication at once (leaving you long times without them, as people have said), aswell as building a big tolerance, so when you do take your prescribed one adderall, you won't feel a thing.
Be careful here, you could very easily fall through the very thin ice to severe addiction.