Personally I prefer the good old fashioned cloak. The Cloak and Dagger does have it uses and while I find it fun to use, I tend to become stagnant and just sit around and watch for the opportune moment, meaning that I take myself out of the match for 2 minutes or more (then again, being a spy is pretty much taking myself out of the match in my case ^^) I do like to use the dead ringer during an initial rush on an attack/defence map, disguise as friendly pyro or something, rush out to get rid of the sticky trap then decloak somewhere behind the enemy lines.
I myself switched back to the normal cloak, since the dead ringer is kinda known now, and the C&D just takes too long for me. Normal has longer cloak time and theres usually plentry of metal or weapons around.