I picked Gambon, but there's actually a scene in OOTP in which I would really want to see Harris being Dumbledore, and that's the appearance of Dumbledore in the Department of Mysteries looking furious. I don't mean Dumbledore appearing via the Floo Network, but a direct realisation of his appearance in the book. I can really imagine the chills and fearfulness I would get seeing Harris appearing as the one person that Voldemort feared. Gambon just doesn't give me enough vibes like that. But on the other hand, Gambon's portrayal of Dumbledore in POA and HBP is just perfect.