I suppose if there is an option to choose the size, then whatever. Though, personally I don't like big avatars (or signatures for that matter) and think a good first impression is important for new users that won't see settings for such things. So if the size increases, I'd almost prefer it to be opt-in.
Regardless, I voted for 150px to split the difference. I think a poll is great though. Whatever people vote is what it should be, assuming we get enough votes to be representative.