While there tends to be reliability issues with the Cambridge model, I really don't think it's often enough to cause concern....besides...warranty.
My pick is the Cambridge. It's a little less powerful but I've always liked their stuff. I've never heard a NAD so I can't really comment on that.
Besides, the Cambridge looks cooler. To be honest, you might not notice a big difference in SQ between the 2. They're both pretty high quality