Adderall XR is 50% dextroamphetamine, 50% racemic amphetamine (mixture of dextro and levoamphetamine). Vyvanse is pure lisdexamphetamine (basically just lysine bound to dextroamphetamine), a pro-drug for dextroamphetamine. A prodrug is something that isn't active until the body metabolizes it into something active. In this case it would be when the lysine is cleaved from the dextroamphetamine molecule.
I take 60 mg of Vyvanse a day. I also used to be on Adderall XR for an extended period of time. I find Vyvanse's time release mechanism to be vastly superior to that of Adderall. Also levoamphetamine (found in Adderall, not present in Vyvanse) is said to be responsible for a lot more negative, peripheral side effects. I've noticed this to be the case. For me, Vyvanse feels a lot "cleaner" than Adderall. There's less vasoconstriction, less cardiovascular stress in general.