Ads Factory was a really nice surprise. What did the trick for me was the way you can customize any aspect of the display through a well thought templating system. I could manage my whole display and change every piece as i needed for my project.
Another nice feature are the payment items the extension provides - pay per listing / pay per contact / pay for featured. It was pretty important for me that i can earn comission after a while from the classifieds that run in my site.
There was one thing that i did not like - the default template uses overlib in order to display tooltips, had to talk to support in order to implement mootools tooltips.
Support was nice and helpful, and i managed to get the job done.
Thanks guys - will add this one on my fav list.