In over 50 years of supporting Liverpool I have never seen a tackler as good as Masher. We've certainly had better footballing DMs or DM-type players (of whom Didi was one), but purely and simply as a ball-winner Masher was the best of them IMHO.
As an all-rounder though, the best we've ever had doing the midfield nitty-gritty hasn't been mentioned yet - Graeme Souness. Hard to the point of viciousness (even I cringed at some of his tackling), he was also a canny short-range passer (not so strong on long passes, but we didn't play that way much anyway) and got more than his fair share of goals too. He skippers my version of the All-Time XI.