Malekko’s Quad Gate Delay may be the coolest. It has some really nifty creative features.
Doepfer’s A-162 dual trigger delay module is inexpensive, popular, and easily modded. I had one for a while because it fires a very hot 10v trigger, ideal for exciting resonant filters and such.
One important difference is that the Malekko is digital and I think it can therefore accurately reproduce the input gate length after the delay, whereas the A-162 is analog, triggered, and generates its own arbitrary-length trigger/gate (knob) at the end of the delay.
Divkid video on the Malekko