On the issue of envelope filters, I've found the MXR Bass Envelope Filter to be my favorite, even on guitar. I've had a few DOD varieties, a Source Audio one (Soundblox, I think?), the Proton v3, and I think another one too? Maybe? I had the Ibanez Screaming Demon wah for a real short bit, but that lead to my previously mentioned near-catastrophe. Went back before the return window closed. It seemed awesome, though! For reference, my ideal wah tone would be Geezer. I don't know that my current tone nails it, but it works for me.
I like the MXR because of the dry/wet volume knob setup. I don't lost any of my "oomph" when it's engaged. And it's pretty versatile, if you like that style of filter. I forget if it's bandpass, lowpass, etc. I also prefer this on guitar to other filters, too. A little goes a long way on this one's knobs.
The DOD FX25B is also pretty great, but they have a volume drop and a very harsh sweep - made me worry about my speakers. I couldn't get the sweep under control without losing the tones I like it for(it actually threw my old Peavey guitar rig into shutdown!). I still have one of these for guitar, but it's been modded by a local guy with an "intensity" control. I didn't do it, so I don't know what all it entails, but I can tell you that I keep the intensity at 3:00 and blend almost at minimum, and there's still plenty of wah to be heard.
