Lifehacker Faceoff: Outlook vs. Gmail—The Definitive Comparison

They gave wins to gmail in some categories (like spam filtering) because it's better than out of the box Outlook. Fair, but irrelevant. You don't use Outlook out of the box.

I'll take Outlook with a Barracuda spam box over Gmail for spam filtering. It's Outlook's ability to be so customized that makes it worth it for me. (Plus mobile is very important, and until Android hits it has a huge lead there.)

They should have at least made extensibility a category.