Yo Leb.. wassup man.. long time no see..
8)
i've owned both the DD20 and the DL4 before, and am currently using the DL4, so here's my 2 cents:
DD20:
$320 after disc. at Swee Lee
Features-wise
Boss buffered bypass
Stereo ins and outs
Has an LCD screen displaying your delay time
Has an LED that flashes the delay time
You need to buy a seperate exp pedal to use tap tempo
Latest version has 'Smooth/Twist' controls to add modulation to your delays
One footswitch for bypass, one footswitch to toggle through 3+1 patches
Technical Opinions:
Lots of buttons to press, and the LED tempo display is nice to have if you are doing studio work/need to do really accurate covers. The lack of a built-in tap tempo is a minus, you'll need to buy a seperate pedal plus a cable to connect it to the DD20, which takes up more space in your pedalboard.
The switching between patches can be a slight drag if you need to change patches quickly, as you'll have to step a few times to toggle through the patches. The loop recorder works very well.
Soundwise
The DD20 has a buffered bypass that works very well. I do not notice a volume drop when the delay is activated. The delays are clean and remain pretty true to your original tone. I had the older version without the modulation controls, so i cannot comment on that. The digital models sound exactly like the Boss DD3.
DL4
about $420 (not sure) at City Music
Features-wise
True hardwire bypass (manufacturer's claim) when delays are off, buffered bypass for loop recorder mode.
Stereo ins and outs.
Doesn't have a screen displaying anything.
Has an LED that flashes the delay time.
Built-in tap tempo switch
Has 'Tweak/Tweez' controls to add modulation to your delays
Technical Opinions:
Less buttons to press, you just have to turn knobs. I don't really miss having an LCD screen to tell me the delay time as i don't do studio work. The built-in tap tempo switch works really well. There are 3 footswitches for 3 individual patches, and you just step on which one you want. no need to toggle through. The added modulation controls are fun to play around with. I find that the DD20's and the DL4's loop recorders are more or less on par with one another, but it easier to do overdubs with the DL4 than the DD20.
Soundwise:
I can attest that the DL4 is true bypass when the delays are off. However, there is a slight volume drop when the delays are on. I am fine with this and i'm not bothered by it as it works with my playing style.
The digital delay models are good, but i find that the DD20's digital delays are more pristine sounding. Those on the DL4 are a bit more processed sounding. The analog models on the DL4 however, are more accurate - they capture the sound of the vintage tube echo, tape echo, DM2, fluttery distorted repeats etc, more realisticallly than the DD20. The option of adding modulation to your delays is fun and you can get some very interesting wacky delay sounds, especially with the filtered delay.
I only sold my DD20 because i went to using POD XT Live. I got my DL4 as i found a used one cheap. I would be happy with either one. Both sound great. One has some features that the other does not have and vice versa. The DL4 costs more than the DD20. The best bet is to test both and see which one suits your needs better.
hope this helps