Which one has better features?
The one i'm gonna use depends on the features available for both at the time. Mac's apps are easier to use and almost always have all the features you need, and usually more than Windows' programs; but if Outlook has better features i will decide for it. I'm an anti-pc person because of their lack of quality but if they make something that is worth the money then i will try it (an example is Windows 7 Ultimate, i have it running on Parallels and i love it)
Bottomline, unless the new Outlook comes with amazing interface and features, Mail will be my choice, it's a great app.