We use both extensively. Some phrases are just too expensive for us in Google, so sometimes we get more traffic from Yahoo for certain campaigns. But typically we get about 3x the traffic from Google as we do Yahoo.

I think both are same, Both have big traffic

absolutely GOOGLE NO. 1

Adwords is the answer. To be frank there is no competition between yahoo and google as google is way ahead.

AdWords will give you higher search volume and is a good B2B market, generally somewhat younger demographic;

Yahoo is much lower search volume in the US, but has a better B2C market than google, much older demographic generally.

May want to experiment with both at some point. Track your conversions to see where your ROI is.

niche dependent an your own efforts also count
but adwords is more profitable for me

My experience is that both are very good search engines, google obviously having the largest reach available, which yahoo is less. Yahoo however I have seen many companies have much higher conversion rates there as opposed to google, especially in ecommerce.

Thanks for sharing. Keep it up.

When you take a look at the status and marketing procedures used fo the top Google ranking websites especially in competitive niches like, Hosting, Domain Registration and SEO, you would find nearly all of the sites also using Google AdWords as it still remains among the powerful traffic pushing plans.

I will vote Google adwords!

IMO, they provide excellent intelligence about the type, number and profitability of searches which can then be used for SEO purposes.

Google AdWords is one of the most readily measurable types of advertising available. The amount of data about your campaign available through Google AdWords reporting is incredible.

This enables the precise tracking of the effectiveness of each search phrase in your campaign. It is easy to determine what the most frequently searched phrases are, what the highest converting (conversion from visitor to lead for example) search phrases are, and what the most profitable search phrases are.