I prefer
Anne to
Ann.
Anne is already a simple, no-nonsense name and it wouldn't hurt to add some flair. Image-wise,
Ann is much darker than
Anne.
Anne also seems friendlier and more approachable.
I only know one
Ann /
Anne - my aunt. While it's a nice name, I don't think I would use it for the reason you mentioned: I think it's quite bland. It's too straightforward with no interesting sounds or letter combinations, and the images I get aren't too exciting.