Its always hard to make these sort of comparisons.Its tried with boxing and football.When I first started doing a bit...,ok,little bit!,Billy Bland's dominance was coming to an end and Colin Donnelly was in his pomp,I think Kenny Stuart had left the 'scene' more or less by then.The thing about Donnelly was that he went onto everyone else's patch and annihilated the local champion and more often than not broke the record.In the late 80's early 90's there were a lot of good runners around,yet he would turn up at their races and beat them,he was simply outstanding.The only real competition outside the lakes for Colin was Keith Anderson,who I remember reading could virtually fly downhill.
Taking everything into account,it has to be Colin Donnelly,he is the best fellrunner ever.