I'm really into the Re-20. It's a really good emulation from my experience...although I've not played the real thing, but it does the modulating. Never played a DL-4, but I've seen so many people with one I feel like I have. I've heard some interesting things come out of it. My friend plays it and he actually has a song where he plays the parts and they are looped into the thing and he stops playing but the riffs keep going all by him and his feet touching the buttons. I favor analog but also like unconventional, it's all in what you wanna do.
The RE-20 will be better for a short slapback delay and standard echo. Similar to a echoplex. The DL-4 will be better for longer delay and different modes like reverse, multi tap etc. Plus i believe the RE-20 doesn't have a Looper.
I haven't tried the Space Echo pedal, but I have tried the DL-4. It's pretty nice.

There are different kinds of echos, and a loop effect. Although, I don't use echo/delays that much so I don't need it. But I recommend it!

Space Echo would serve you better as an all around crazy sounds pedal (especially with the expression pedal), and the DL-4 would be a better actual delay