I went online and begin receiving immediate hits and response on my local google marketing program; I’ve waited three days on yahoo & have 8 impressions using the same words & phrases that I am using on google. Do they discriminate or do they just have an overmanaged system?!
If you are talking about pay per click advertising (Google Adwords, Yahoo Search Marketing), you don’t want "hits." You want clicks that resolve in sales conversions.
In my experience, Google far outperforms Yahoo in terms of volume of clicks and conversions. We blow through our Google budget 3-4x faster than Yahoo and the leads are slightly higher quality.
Don’t even bother with MSN or Ask. They don’t have their acts together yet.
Good luck!