There are two questions which affect my answer.
Do I get to be an avatar of this superhero on Marvel Earth or do I get the package on real world Earth? If I have to go through the process of these characters, I guess I'd stick Captain America because he is slightly closer to me in personality than the other five.
I think I'd rather just be me with no power than be an Avenger on Marvel Earth.
But let's assume I am basically me and I get to be on the real world Earth on 2022.
Hulk: I have many personal flaws, but anger was not often a problem for me. I am slow to anger and rarely act out of impulse. That said, I fear this would make me worse at being Hulk. One, I'm not used to flying off the handle so I might have more trouble dealing with it. Second, I might be too mellow. Hypothetically, there could be something coming that requires Hulk smashing and Scalenex is too calm and/or lazy to "go green".
The real world is complicated. I doubt I can make life in mainland China better by Hulk Smashing stuff.
Thor: I think Jaime Alexander (Sif) is slightly more attractive than Natalie Portman (Dr. Jane Foster). Also, Jane is going to age and die really fast compared to Thor/me. Also a warrior maiden fighting besides my side is more useful to someone like Thor than a "brilliant scientist". Considering how much more advanced Asgard is than current year Earth, that would be like one of us dating the smartest person in 1450.
Thor is strong and handsome and has good control of his powers. The main disadvantage is a miserable backstory but if I could have Thor's power and position with my backstory that's not a problem.
I'm not sure if Asgardians are allowed to meddle in Earth politics. If I cannot get the backing of the rest of Asgard (or New Asgard) there is only so much positive things I can do throwing a hammer at things. Same problem as Hulk.
Black Panther: Cultural appropriation not withstanding, his powers aren't that different from Captain America.
But he is the prince of Wakanda. A nation that cured cancer, they are just not sharing it because they are selfish dicks. I'd love to cure cancer world wide.
I'm not sure if Wakanda can contain the CCP or make things worse by aggravating them, but curing cancer alone is more than enough good for one person to do.
They have other awesome technology too, but most of it could be turned towards evil ends in the wrong hands. It'd be hard to make a cure for cancer evil though I suppose it can keep evil people alive longer. Since I lost a lot of family members to cancer, I'll risk it.
Iron Man: Forget the suit, you can do more good as a billionaire philanthropist inventor. That said, I think Wakanda's technology is better but Wakanda's ancient laws are such that even the prince can not share medicinal secrets, I guess Iron Man works.
I'm not sure I'd use the suit. Ironman 1, the villain uses the suit's technology to make something evil. Ironman 2, the villain uses the suits technology to make several evil things. Ironman 3, a guy Tony Stark accidentally insulted at a party did a bunch of villainous stuff...never mind I hate that movie. It insults US veterans and the handicapped, but nevertheless the villain was created by Tony Stark. So was Ultron, he was a Stark Industries villain. And he kind of started the Marvel Civil War. Maybe the world doesn't need a Tony Stark. The closest thing we have to Tony Stark is Elon Musk and he is deep in the CCP's pocket. I'm not sure I am smart enough to be Tony Stark and not make things worse.
Doctor Strange: I cannot imagine I could use that much power responsibly. I wouldn't take his power set unless me doing so would prevent someone worse than me from taking it.
Captain America: It'd be cool to be taller, stronger, faster, and exactly as handsome as I am now. That said, I don't think someone like him can do more in the the Current Year real world than be a figurehead.
