I've used to own 2 TC D2's and I got rid of them. They didn't impress me much, plus they're rack units. Which isn't bad perse but does require a more complicated setup on your part if you go with them.
The Nova Delay on the other hand is the bees knees IMHO. I was one of the first to get one. I like their sound way better then the D2, plus its a stomp pedal, so no need to invest in midi controllers. It can do analog, tape and digital delay, all with modulation. You can store up to 9 presets and if you use stereo delay you can offset the left channel from the right, the way Edge does. Which makes it excellent for U2 covering purposes. It's not the delay pedal to end all other delay pedals, but then again no delay pedal will ever be. Which is why I got three different delay pedals including the Nova on my boards.
The only delay pedals I can think of that are as versatile are the Line 6 delay modeler and the Eventide Timefactor. And they cost more.
As for the D2 vs. Nova Delay comparison:
D2 Delay: 19" rack unit, costs way more and needs a midi controller. Has 6 kinds of delay but these are only digital, 50 factory settings and 100 user presets. The best 19" delay unit currently on the market, but only because the 2290, Korg SDD-2000/3000 and the Line 6 Mod Pro have been discontinued.
Nova Delay: Stomp pedal, costs way less then the D2, doesn't need a midi controller. Unlike the D2 it can also imitate analog and tape delay, comes with 9 factory presets that can be overwritten with your own.
