Mary Ann. It's not just the fact that I find her adorable, it's also that Ginger's personality turns me way off. Mary Ann seems more like a confident, intelligent, funny, sweet person, one who is capable of taking care of herself, and I find that immensely appealing.
Mary Ann is undeniably hotter and sweeter, but I feel there's a lot to like about Ginger's personality once you look past the surface. True, she was initially written as a vapid Marilyn Monroe clone, and that's a type she later reverted to when recast for the animated series and reunion movies, but for most of the series, Tina Louise brought a great deal of intelligence, canniness, humor, and strength. She wasn't just a sex object to satisfy male fantasies; she was a shrewd and self-possessed woman who understood, embraced, and utilized her own libido for her own reasons and goals.