I don't think a poll like this has been made; I didn't find anything when I searched "favorite Beatle," at least.
I am using the various Beatles' solo works to aid me in my choice, so feel free to, also.
Only a few months ago I would have said John, but ever since I listened to George Harrison's All Things Most Pass, I have to go with him. That album is just brilliant. While I like a lot of John's solo stuff ATMP just blows it all away. Plus, George wrote my favorite Beatles song, "Something," and I've always liked his songs in general.

