Reach
Reach -- Major Advantage: Google
In terms of search market share, remember that Google typically outscores Yahoo something like 60-22 percent, depending on the rating agency. Your Yahoo spend should be less than your Google spend in most cases, but yahoo is still the number two player.
Top-Level Campaign Settings - Slight Advantage: Google (But Leapfrog is Good)
In both systems, advertisers can see overall campaign information like CTRs, clicks, average CPC and overall costs. In Panama, there is a little more information provided in the dashboard tab (the default campaign information screen). Advertisers can see a graphical display of the last two weeks of account activity. The dashboard also alerts advertisers of various account events like payment notifications, editorial review information, bulk upload information and incomplete campaign notification, to name a few.
Google has recently followed suit with an "account snapshot" screen (similar to Yahoo's dashboard), apparently now in limited beta, that we personally find useful. It goes to show that this game of "leapfrog" is beneficial to us, the customers.
In Yahoo, the default date range is a two-week period (always). In Google, if a different date range is selected, it will hold through to future sessions.
Account Structure - Even Score
Yahoo has basically copied Google's approach, calling "campaigns" campaigns, and "Ad Groups" ad groups. Advertisers welcome this. MSN will also move to using ad groups in the new MSN adCenter (currently in beta). In the current MSN adCenter system, newly submitted keywords and ads are called an "order.'
Ad Copy and Rotation - Even Score
Both Google and Yahoo have powerful testing capabilities now. Although many will continue to find Google's more intuitive because they're accustomed to it, some may see that Panama has a small edge here because it's easier to associate distinct ad copy with search and content targeting. Yahoo now allows you to set your own display URL rather than inferring it from your destination URL. In other words, it's non-annoying, just like Google.
Next: Content Targeting