I've no problem with Gravatar - until I decided to change my photo after several years, and found that I now needed a WordPress.com account. That got my goat a bit.

Plus, if you build a site where you want author images just for that site it makes more sense to use something like WP User Avatars - which is what I use on my site and others I've built - than force users to visit a different site to update the author image for their own site, which is somewhat counter-intuitive.

Gary