First, the one with the best marketing. Second, good luck on your website because I have a horrible experience being an 11,12, or 13 year old with a site getting well over 10,000 unique visitors a day and millions of hits each day due to the type of site I ran. Anyway, yeah, I tried a couple of good advertising companies and they all went out of business. This was during the time when the economy was going down and I didn't really think it affected me that much until recently.
Look for the one with the best marketing and not pay out rate because you may have a $.20 per click, but what if the ads are crap? Whose gonna click on them but yourself? No one. You'd rather get paid $.05 per click but with very good advertisements and display so it attracts others. Take my word for it, if all you look for is price, you're not going to get far in it.
As for which advertisers, I have no idea since i ran mine a couple years back and those are all o ut of business now...