I think Richard Harris was a much better Dumbledore than Michael Gambon for a couple reasons:
Looks - Richard Harris looks a lot more iconic than Michael Gambon, with the long flowing beard rather than the scruffy beard bunched up at the middle. Also Michael Gambon’s weird hat is not it. 😬
Personality - Michael Gambon is super angry when he plays Dumbledore, and the real Dumbledore never shouts like that. Richard Harris on the other hand is nice and calm, just like Dumbledore is supposed to be.
Michael Gambon never read the books, which is something I don’t think any actor in the movies should do.
I think Maggie just nailed the performance. IMO Flitwick and Sprout were a tiny bit overplayed (at least in the first films). Lupin was (I'm very sorry) too old, like all from the marauders generation and (just a personal preference) I didn't like the way he spoke.
Harries was quite good but I think sometimes underplayed. Maggie was the one who was most accurate