If price truly isn't an issue for me it's gotta be a Mutron iii. It's the sound in my head when I think of an envelope filter, I mean COME ON, it's what Bootsy used, it's what Jerry Garcia had his g****r modded for, it's what Stevie Wonder played his clav through on Superstitious. The Moog is a great studio tool but I had a chance to play a real Mutron once and that thing is the TRUTH.
My honorable mention goes to the one on my board right now which is a Mojohand 443. VERY natural, works well with whatever you throw at it (fuzz, octave, etc.), and has a range of sounds without ever sounding bad. Can get aggresive but I never leap out of my skin when I turn it on. I think it should get more love around here, I tried the MXR BEF, Source Audio BEF, HAZ Mutron, Aguilar Filter Twin, DOD fx25, Keeley Neutrino, EBS BassIQ, 3leaf Proton, EHX Enigma, DOD 440, and Mojohand 442 before landing on it.