This article may be a year old, but it talking about Windows 6.0.
The article is a non-biased view of the two and lists many shortfalls, not just the positive points.
It eventually claims Blackberry to be the winner:
Grace Aquino: BlackBerry has also evolved, especially on the multimedia front, but ultimately we prefer it over Windows Mobile because it doesn't feel like it's trying to do so much. The OS is snappier at opening and closing applications and surfing the Web, and it has lots of helpful shortcuts to make already intuitive software even more useful.
But the reason "Windows Mobile feels like it's trying to do too much" is curious. Do we not want a device that does everything? Maybe this is the crux of the matter for people.
* If you want a business device that does everything, with the price of a steep learning curve, choose WM.
* If you want a business device that just works and has a very small learning curve, choose Blackberry.