Test them both out and see which converts better for you. In my industry, at least (tech), AdWords can deliver more traffic but there is also more competition with certain keywords. I believe Yahoo! also has a higher minimum cost per click. AdWords also has the whole AdSense side which is more robust than the Yahoo! publisher network. But it's all about return on investment ... so you never know until you try.

If I were just starting out, I would test Yahoo first because it is easier to get your ads on the Yahoo search engine.

Google AdWords can deliver a lot of traffic, but their "quality score" formula makes it difficult for some people to get their ads shown on Google.

Make sure you have a good stats program so you will know what the traffic does once it enters your site.

Google has better geo-targeting abilities than Yahoo! So if your target audience is outside Europe and the US, then I believe Google is the way to go.

AdWords is the route to go. I agree with what mauconline posted.

I believe that adwords can deliver a lot of traffic, but you shouldn't stop researching for other methods, try experimenting its worth a try..

Adwords is the best one as for as concerned me..

I have been using both Google adword and yahoo search marketing for years. The thing which exactly matters is the ROI.
The search engine performance depends on what type of product/ service you are marketing.
I observed that google adwords is giving more ROI(atleast in technology business) then yahoo. In yahoo the CPC are comparatively low than Google adwords.

One more thinng I wann add. most of the advertiser don't want to go much for yahoo search marketing because yahoo's reach in pay per click marketing is less and the advertising platform is soo complicated.

Thanks,

http:/www.clickadtrix.com

In this recession time both google adword and YSM suck.

Adword becoming just more competitive so you may find rate differences from others, however as far as content matching is concerned Google shows more natural results than Yahoo! Search Marketing, this is just my personal view which may differ from others.