Definitely Windows 8
Runs better/faster on same hardware as Windows 7.
The integration with Skydrive/mail/calendar is outstanding, and gives you free 7GB online storage (25GB if you have used Skydrive for long time - and this is the same for win7, except for the smooth integration).
The new UI/Metro interface takes some getting used to, but now i will not be without it. And it's really nice way to have instant feedback in the from RSS, Mail, Calendar, Updates to your apps etc.
Search is also really great - just start typing from the metro interface and then you get instant feedback, and the posibility to search directly in an app such as ebay, mail, app store etc.
I usually say to people - give it a week or 2, and you find out if it Works for you.
Furthermore the way Win 8 handles multiple screens, the new Explorer, Windows 8 to go and most important (to me) is the built-in Hyper-V that just Works great for Virtual machines.
There are a lot of different opinions about Win8, but if you are unsure, then try it for free for a couple of weeks, and if it doesn't Work for you, you can always fallback to win7.
And by the way - you don't Loose the desktop - you still have it there - it's only the "start-button" - but i really thinks the new ui/metro interface is that much better than the old start-button.