As far as I can tell, at the present time, yes .. my DK is my new main.
My priest? (70) After years of healing, looking at charts, and missing most of the action, I've grown weary of it.
My hunter? (70) It doesn't seem like the same type of character that I started playing years ago. The new exotics seem more like pets on parade. The glass seems gimmicky to me now (my own personal opinion), and my level of enjoyment, sadly, has deflated.
My mage? (71) Still possibly in the running. She will probably pave the way on my learning curve through Northrend, as I observe the tanking in those instances.
But I have to say that my DK has taken the top spot in terms of fun factor.