Generally speaking, for every 100 visitors Google sends your way, Yahoo/Bing will send you 10 to 15. Don't try to make it "this OR that" ; rather try to make it "this AND that too" Where to promote depends on where your target demographic hangs out, so do not ignore the social web of Facebook, Twitter, etc or other sites like Youtube. ninja_va
google will send more traffic, but you must ignore yahoo and bing now.... they can increase your traffic by 20-25%.
In all reality it really depends on the day. Google seems to get more traffic but yahoo has been successful for me also so you really need to try them both.
Even though Google will give you way more traffic, but Yahoo usually drives better conversion rate. If you are promoting on a high competition keyword with limited budget, then Yahoo may suits you better. But if you have all the money you can spend, better off to use both or just Google.
I think yahoo and google produce good USA traffic but if YPN then yahoo give more usa traffic because they take only usa publishers.
Google generates 70% of traffic from USA and yahoo generates only 10-20% of traffic so go for google if you getting ranking in google then you will definitely get good amount of traffic from yahoo
Google will send more US traffic than yahoo since more the internet user in US are using yahoo Yahoo only send good traffic from certain country which has more user such as Japan, China etc
Google is normally best for US traffic and UK traffic is also getting better with Google Yahoo will send mostly Asian Traffic If you want more traffic generally, I'd use a search engine submitter and you'll get the best from all search engines!