I have:
- Doepfer A-141-2 VCADSR (ASDR/LFO) module
- 4MS PEG (Dual Envelope Generator)
and I also had, but sold off - Befaco Rampage (Dual Envelope Generator)
I'm fairly new to modular, but so far, I like both in different ways.
So far, I use the Doepfer more so for applying ADSR to audio signals, and it seems fairly versatile with separate CV inputs for A/D/S/R, variable CV triggering levels for each, End of Attack / End of Rise triggers, Inverted output, and a couple other potentially handy options. Be aware that like many Doepfers it is a sort of obnoxiously deep module though, won't fit in a shallow skiff.
The 4MS PEG was frustrating at first (as was the Befaco Rampage) because I expected it to work sort of like an ADSR (or an AD anyway) and was trying to apply it mainly to audio signals. That can work -- sort of -- but not very well. I got the impression it was really intended more to manipulate CV levels as opposed to directly effecting audio signals, and once I started applying it that way, it came into its own a lot more so. It's way less predictable and a lot more finicky than a digital equivalent would be in a DAW, but I guess that's true for pretty much all modular, and now that I've gotten the hang of it I like it quite a bit. It's very versatile and can add a lot of complexity to a patch. The Befaco Rampage was pretty much the same thing, I only had room for one at the time and chose the 4MS because I've generally liked the modules of theirs that I have.
I'm looking into more ADSR options myself, so interesting reading through this thread to get some ideas.