Hamann and Berger definitely were underrated, such a shame the latter was blighted by injury.
In my earlier days of supporting LFC I'd go for Gary Gillespie. Fantastic defender, seemed about 7 feet tall but so elegant on the ball, never made a mistake and only failed to make about 600 LFC appearances because Hansen/Lawrenson were the preferred partnership. Also he had a few injury problems as well.
In recent times I would have to say Javier Mascherano. Yeah, I was really p...ed off at the manner in which he left but such a strong guy (especially for his size), never shirked a tackle and as hard as they come in the modern game. By that I mean he took whacks as well as giving them without rolling around on the ground, just grimaced and got on with it. Distribution was good, had a will to win which sometimes overflowed with rants at the referee but every successful team needs a player like Masch. Barca is the only starting 11 he couldn't walk into.
