I say Gentle Giant for my personnal tastes, but I think it all depends on what you focus on. Instrument masters: Yes and maybe King Crimson. Musical theory masters: King Crimson and Gentle Giant (and others, but those are the most popular). Diversity: Moody Blues??. Togetherness: I'd say Genesis.
Anyway, I think my point is clear: I think that the question is not clear enough.