I really like Michael Gambon as Dumbledore.
I would never fully choose between Michael Gambon and Richard Harris as to which is the best Dumbledore because I don't think it's fair. Both actors have their good points in the role anyway and I feel that most of the bad points of Michael that other people point out, aren't entirely his fault anyway - and maybe even not his fault at all.
For example, the "shouting" in G.O.F - I would assume that was written as such in the script anyway, and even if it wasn't, then it was down to the director to tell Michael to be more calm in the scene. Or even up to the editor and/or director to use the calm scene when the film is finally being put together.

I also think the robes are a problem.
Richard Harris had a lovely rich, warm red that helped make him seem like a warm person and made him stand out.
With Michael's robes, he blends in too easily with the background and it's always made me think that the actor himself would feel cold in those robes! *lol*