They are very similar, but the euphoria with Adderall is significantly less than with meth or other speed you'd buy on the street. For some people meth might be an effective substitute, but I think most people would find the high and the side-effects too distracting. Plus, that euphoric high increases the likelihood of abuse and addiction.
I'd add that the people I've known who did a lot of meth tended to have physical health issues and looked like shit, which was not the case with the people I've know who abused Adderall.
Method of administration affects the time delay for euphoria. Smoke > Shooting > Eating.
People who do a lot of meth (or drugs outside of a prescription) tend to do as much as they can purchase and/or tolerate.
When you see someone who has a doctor (dealer) that gives them as much adderall as they want, illusions of differences between the two drugs rapidly fade. I'm talking about 100+mg a day, I've seen it happen, still have 50mg adderall pills from the person in the story.
I'd add that the people I've known who did a lot of meth tended to have physical health issues and looked like shit, which was not the case with the people I've know who abused Adderall.