Now your probably thinking, AdSense or Chitika? And I would say, if you only want to use one, use AdSense because more people see it and it generates more money than Chitika. If you can use both (and you can; AdSense's T's and C's indicates you can but people have checked and it is allowed) go for it! Chitika's ads look much better than AdSense units mainly because they have a small picture - this could increase the amount of people who get drawn to the ad, and click on it.
I will say more about placing the ads on your page in my next post.