Belinda - not the best housemate ever or anything, but nobody ever mentions her, even when talking about BB9 but she was a really interesting casting choice and the only good "older" woman they've ever put in the house apart from Lesley (who lasted longer but still gets lots of love).
Craig Coates was underrated for years but I think he is finally getting some appreciation
Derek was loved at the time but doesn't seem to get mentioned much nowadays even when talking about classic posh housemates
Most overrated: Heaven (she wasn't that interesting really), Aaron (he's a decent old-school winner, but he's not the Messiah), Freddie (annoying), Sam Pepper.