jazzcat,
I can't speak for everyone but tpgs eat way too much bw for my tastes and the conversions are much lower than my free sites. You have a one chance do or die shot at the surfer with a tpg, where with a free site you can ideally pretty much push up to 12 out going links and they can go to any combo of advertising you want...ex. fpas to sponsors, your own link lists, your own sites (avs perhaps), etc. Obviously there is money to be made in tgp or there wouldnt be that many out here doing it, but for me I like to spend less to make more, and that wasn't the option that tgp offered me personally.
Good luck deciding....hope you figure out what works best for you
