I have never had any issue at all with Vista. However 7 has been plagued with issues from day one for me.
Moreover, Windows, no matter the version, is a desktop OS. If you want to use a mobile device, be it a tablet or a laptop or the various versions thereof, windows should be your last option. The other offerings (at least on the linux side) do a lot better job at conserving battery life, and using power save features. Not sure about Andriod for tablets, but I would bet being a smartphone based OS that it would be good with batterys too.