I use that old "Do unto others..." philosophy and thus I am a picker. I live in a house and there is at least one neighbor's dog who keeps pooing in my yard and his owner is definitely a leaver - and it is ANNOYING!
It is one thing to have your own dog's poo in your yard, but totally another thing when other dogs (and their owners) treat your yard like their toilet. Plus, I am not a picker by pure joy of the act, so picking up additional poo really sucks! It is not only rude but unsanitary since many nasty organisms can be passed from dog-to-dog through poo.
So as unpleasant as it may be - I pick.