Is both not an option for you? I personally prefer AdWords utilizing regional and without content matching. But I would try Overture as some industries seem to do really well with them.
Usually the same ones that tend to see more traffic in Yahoo. One example would be teen oriented sites like smilies and IM software.
I agree that adwords is the easier one to use, but in some cases because it is easier it is also more competitive. I have many times encountered keywords/categories where the cost of a click on adwords is so high that I cant possibly make any money on sales. Sometimes Overture can provide an opportunity for lower bids. For one specific product I sell there is no competition on Overture while Google has lots of competition. Sometimes the situation is exactly the opposite. Also, I believe that there will be changes in Overture's interface over the next few months - so I would keep an eye on that.
I would kick off with Adwords first of all just to get a feel for the whole PPC thing. Overture can be tricky unless you already have an idea of what your doing. Adwords is much easier to set up and get going.
Here are a couple of other facts to help you with your decision. 1. Overture (now called Yahoo Search Marketing) will charge you in advance for your advertising and you whittle down the amount in your account as click charges add up. Google charges you periodically after you ring up click charges. 2. Overture will charge you a minimum or $20 per month whether you use it on click charges or not. You can pause all of your advertising, but you will still pay the minimum fee. Google has no minimum and you can pause your ads without incurring a minimum fee. 3. It generally takes two or three days for ad approval with Overture. Google ads are live within a few minutes. 4. I personally find the Overture user interface to be confusing and I frequently have to hunt for information. The AdWords interface can also be a bit confusing, but becomes much more intuitive as you learn to use it. I use both and I think there is more of a logical structure to AdWords. 5. Google has extensive tutorials for using AdWords. It can literally take days to go through them all, but you can learn a lot. Overture's tutorials are structured more like FAQs. There are people who do very well with Overture, particularly for the niches mentioned, but I think most people use Overture as supplemental advertising in addition to AdWords.
Yep! Really good summing up. Green from me! It's a minor point but if you do not run your ad campaigns at all during the month, you will not be charged the minimum amount. Partial use during the month incurs the minimum fee, even if it is only for a day.