I've got a DD20 on my big board, DD7 on the small one. I've been through all the other popular ones, but kept coming back to the DD20 for the mod delay sounds and combination of features.
DD20 is in a parallel loop with a line mixer so I can blend it in ... DD7 takes an expression pedal, though the parallel approach definitely sounds better. Mostly I use the mod and tape delay.
There are a million delays out there, so you really need to figure out what specific features appeal to you. Eg: delay types/presets/physical size/display/instrument or line level/tap temp/expression pedal/kill dry ... and so on. Also makes a big difference if you're going to be putting this in front of your amp vs in the loop.