I think I would have wanted to be Katherine of Aragon least. Sure, she had the longest time in the sun, and her head wasn't chopped off, but it was particularly brutal for her because she had such happiness, and security, and then without warning it was all over. Not just her marriage, but her whole world, her religion, her daughter. The whole cherished part of her life gone, and she had not done anything to deserve it. She had practically killed herself trying to supply a son, but either miscarried, or it was a still birth, or the son didn't live very long. She expected that Henry excepted the facts, but then he goes and divorces her so he can have his male heir, by Anne Boleyn. And she never didn't use her wisdom like Catherine Howard, nor did she provoke enemies like Anne Boleyn. She did her best, but it wasn't enough for her, and she had to endure so much pain, and it lasted long.
So for these reasons, she is who I would like least to have been. And her daughter Mary I wasn't one of England's better queens, so even in posthousmous memory, she suffers. She is so often seen as old, dowdy, and boring as well, because people forget that she had a youth, and what she was like in it. As for who I would have most wanted to be, of Henry's wives, that's another post.