I had both, and I'd go with the DC. I think the DC has a better clean channel (and that channel sounds better overdriven than Rhy2 on the Mk IV), reverb is waaaay better, and Ch2 on the DC smokes the MK IV for gain, sounds better to my ear without the GEQ, I like the lower-mid emphasis over the nasally sound of the IV, and is less compressed.
The Mk IV/Strat thread got me thinking about how much I disiked Strats through my IV. So tight and bright, thin even.
Oh yeah, it's a lot lighter.
DC all the way.