Hi I must say the deficiency of adsense crawler. they really suck into showing relevant ads. I am totally dissatisifed with the ads on my page sometimes even no ads when so many advertisers are available. Google search is okay considering if you don't like itm you can find another one. However adsense has direct impact on peoples' money and it is not terrific to know that Google can do anything with our money. Microsoft is doing nothing to compete With Google in Adsense and spent most time destroying open source stuff by competing in browser and server side language which cost programmers huge time loss.
Okay! Then, which one do you think is better than AdSense? Google AdSense has the most targeted ads. No other program has that many advertisers, ads, CTR and CPC. btw, Whats your niche? Google will not place the related ads if there are no ads available relating to that niche and keywords you used. It also matters when you place your ads in iFrames. Just be satisfied with what you have now as there is no better alternative for that. If you are from US, then, try YPN!