If you have a million bucks to run your ad campaign, this article is not for you. If however, you are looking at running an ad campaign on a tight budget, pay attention; the best value isn't where everyone says it is (disclaimer1).
Of the three small budget online advertising options tested here: Microsoft Adcenter, Google Adsense and Yahoo! Marketing Solutions, guess who the surprise winner is! Screen-shots below:
I guess I do not really need to say anything. The results speak for themselves. If you are still scratching your head, let me know in the comments 
Before you draw a conclusion, please read the disclaimer1. All the three experiments were done on similar budget, near similar constraints and an (almost) exact timeframe.
Google Adwords tops out in experience. Seemless integration, less than 5 minutes from get, set to start delivering.
Microsoft AdCenter fastest to empty out the inventory! Spend cap reached in just 5 days!
Yahoo! SM takes 4 days for editorial approval. 4 days! but once approved, the results are very impressive.
AdWords has the costliest min bid for keywords
Yahoo! SM is the only one where keywords change their position from 3 all the way to 20 (within a single day!)
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This posting is provided "AS IS" with no warranties, and confers no rights. Your results and experience may differ from the author's and you assume all risk for your conclusion. This article has not been read or approved by Yahoo!, Google or Microsoft