Not necessarily your favourite / least favourite (but of course some may overlap). I tried to stick to one because once I start listing housemates I go on forever.
BB5:
Overrated: Jason (almost said Victor but Jason was worse and was runner up so...)
Underrated: Becki
BB6:
Overrated: Anthony
Underrated: Mary
BB7:
Overrated: Nikki
Underrated: Sam
BB8:
Overrated: Brian
Underrated: Shabnam
BB9:
Overrated: Rex
Underrated: Belinda
BB10:
Overrated: Sophie
Underrated: Hira
BB11:
Overrated: Josie
Underrated: Sunshine
BB12:
Overrated: Jay
Underrated: Heaven
BB13:
Overrated: Conor (he had enough fans to survive those evictions)
Underrated: Lydia
BB14:
Overrated: Gina
Underrated: Charlie
BB15:
Overrated: Helen (again, unpopular with a lot but had enough support to win)
Underrated: Danielle (very nearly said Christopher but he did make top 3 at least, and Danielle had a rough time with viewers pretty consistently)
BB16:
Overrated: Danny
Underrated: Eileen