I'm not much of an FX guy... I dabble sometimes, but an envelope filter is probably my "if you could only have one pedal" pedal. I've sampled a few. Here are my thoughts for what they are worth. YMMV.
MXR - the purple one - Cool, and easy to dial in. Very wet, but too many lazer sounds. Very processed and not very natural sounding, but a good pedal if you are going for more of that synth type thing.
DOD FX25 - apparently there is a big difference from the old ones (avacado green = good) to the new ones (sparkle green = bad). I got one of the newer ones used for real cheap and did not like it. Massive low end, and really hard to get the filter to open. I did not find it to have good touch sensitivity. I gave it to my guitar player, and it sounds pretty good for him. Cool if you are going for a dub / synth / massive low end thing - IMO. Other people love them.
EHX micro Q-torn - pretty cool. A bit of the lazer beam thing going on, but you can kind of dial that out a little bit. This one sounds pretty nice and has nice response, but you kind of have to find a sweet spot with it or else you will get some not so great resonant peaks. Middle of the road - not bad.
The winner for me is the 3 leaf Proton. By a mile. Hands down. Very transparent. Easy to dial in. Great touch sensitivity - you can "play the filter". Great range of sounds. Doesn't get the nasty resonant peaks. Very wet and funky. I have the old V1 pedal that has the two different filters. The BP or HP is pretty useless and has been removed on the V2 and replaced with some other control.
I just got a Keeley Nutrino - which I have not even hooked up yet. When I do, I will probably do a A/B compare thread with my proton. It looks to be about the same as the proton in terms of design and features... they are both Mutron III clones.
Have also sampled the Aguilar - cool, but pretty subtle and the up and down filter at the same time is kind of weird - cool sounds, but not really what I was looking for.
Sampled a Malekko E Filter -- tiny little pedal. Pretty cool. Good sounds. two knobs. Easy to dial in a sound. Nice touch sensitivity. Wet and funky.
Played a Bass Balls once -- kind of in a different category and didn't really interest me much. All lazers.
Filters are such a personal thing, because it's all about how your hands interact with your bass and the filter. You really do have to "play the filter." Anyway,,, Just all IME and IMO.