I voted for even smaller ones, any larger than they used to be is just a waste of space. I know one of the arguments to make them larger was to better show off the avatar art, but that's just a sign of a bad artist.
Edit; Just to clarify; not meant as an attack on anyone on GH who does make avatars(1 or 2 people from what I've seen), they make decent art, it's meant as an attack on one of the arguments used to justify the increase in avatar size.
That said; if you need 150+ px avatars for it to work, then it's bad avatar art. Not bad art, just bad avatar art. Avatar art is about getting stuff across with limited space, not how much you can cram into the space you have.