I agree that PW is the way to go. It's pretty easy to get 0.01-0.02 per click and it's nice to be part of the webcomic community that it supports. This way people who really appreciate webcomics will be visiting your site.
My experience mirrors some of the other sentiments I've seen in this thread, namely I get the best response from advertising on "mid-level" sites. I never seem to get my money's worth when I advertise on a site that costs more than about $0.2 a day.
What's everyone else's experience?