I liked Sir Michael John Gambon better personally. I thought he just seemed stronger and more confident. I think Richard Harris was sick though, so that might explain why he seemed "weak" to me.
I liked Richard Harris better. He just seemed more like how I pictured him to be when I read the books. I was so sad whwn he died. Like, the softer voice just seemed more how I pictured him. I know most people like the second one better though.
Re: Dumbledore