Hi there, I've tried both, and I currently own the DD20.
For me the main importance was that whatever delay pedal I use, the last thing I want it to do would be to alter and color my tone. I felt that the DL4 did that, I always heard a slightly volume drop when I kicked it on. No such problem to my ears so far with the DD20.
Another consideration was the footprint of the pedal. The DL4 is pretty damn huge and oddly shaped. The DD20 has a nice compact footprint, probably about the same size as two boss pedals put side by side.
But I must say that if you're looking for tripped out spacey effects then get the DL4, there's loads of stuff you can toy around with. But if you're looking for a no nonsense delay pedal for adding texture, atmosphere, to your playing and solos, then get the DD20. You can get really quality repeats with the DD20, very rich sounding.
I love the fact that there's a display on the DD20. The analog setting on the DD20 sounds awesome as well if you're into analog delay type tones. My only gripe so far with the DD20, there are 4 patches, 5 if you count in the manual patch, you can only cycle through them in one direction.
Meaning if you go to patch 1 and then to 2, you gotta go through 3 and 4 to come back to 1. Which typically translates to quite a bit of tap dancing. Not really a problem, just something which takes a little getting used to.
All in all the DD20 imho is probably the best delay out there you can get from the sub-400 range.
Try them both and if possible try them side by side.
