Well, since I only own three modules at any given time, as I'm a bit of a utilitarian in this sense - if I cannot switch it on the fly whilst playing live, I really have no true use for it. If I need more variety for recording, the studios we record with have mountains of awesome gear. So, my current 3 are, by default, my favorites, so far at-least, lol:
1) JF Vybe Deluxe - I can't imagine a 'clean' to lo-gainy module that could suit me or my playing better. Awesome mod, and very versatile.
2) Salvo Mash-All - I use this only in the Plexi mode, and hit it with a Klon-type OD out front - awesome, warm, mid gain/crunch all day.
3) JF Cutom Blackout - A modded Erect - has some more mids and more aggressive character. Love this mod for high gain stuff!
I've rolled through a whole bunch of mods, and settled on these for the time being. My previous favorites included my prized JF R'Verb and SL-OD100. Both great modules. I also loved the JF XTC SE that I had for a bit - just had too much overlap with what I had at the time.
I have a SG MK22 on the way though, so hopefully it'll unseat that Mash-All!