I typically use Voluum on my campaigns, but I decided to try out PeerClick about a month ago and I am really liking it.
The reports are fast and creating a campaign is very intuitive. Alex is super helpful and friendly.
I have had a few issues with the traffic source templates that they have and I think it's important that someone from PeerClick check and update those often.
I really like their Bot reporting build into their reports.
My one BIG request is some sort of automatic optimization for split testing offers and landing pages. I've been told they are working on it. That will be a really awesome feature that will help make PeerClick my preferred tracker.