There are too many modules to compare them all. As far as the modder's go, these are my basic opinions-
Salvation- I've had about 15 salvo mods over the years. I seem to like Salvo's the most. They sound very close to the actual amps they're modeling. While some of them haven't been my cup o' tea (Mash-all), many of them are fantastic stuff. I think a Masholdano might be in my future. The downside to Salvation mods are the wait time, cost and addiction to the mighty fine modules Salvo offers.
My all-time favorite salvo mod is an early Custom 3.
Jaded Faith- I've had 5 JF mods. As you may well be aware, Rob is an active member on the forum and tries to answer questions about his work as best he can. For a customer based in the USA like me, the wait times to get a module aren't comparable to Salvation. Rob might take a month and Anthony might take 3 or 4 to get an order done. Also, his prices are a bit less and shipping to and from is simple and quick. The JF mods I've played are impressive and have lots of tonal options. I think rob does "touch sensitivity" a bit better than Salvation. Rob's modules sound like modded amps, instead of "it sounds like the stock amp". He also has some clean modules which are unique in the MTS community.
My favorite JF module is the Plexi/Tweed. It takes dirt pedals like its nobody's business when set clean and can do RHCP to Thin Lizzy Tones. =)
Friedman- I've had 2 Friedman Brown Eye mods. For my taste, I had to run my Power amp tubes very hot to get the module to sound good, which threw the other mods I was using out of whack. If your name is George Lynch you're a Friedman Fanatic... if its Rossness... um... you're not
Voodoo- Ive done 1 custom mod with Trace (based on Third Eye Blind's debuet album) and got a plexi module in a trade. Trace was a great guy to work with and his turnaround time was about 2 weeks. Trace also does "touch sensitivity" very well. His modules are more basic and have less tweaker switches, but that makes me work with the EQ a bit more. Voodoo mods also have an interior gain trim pot to add more are less gain depending on how you want the module to feel. As far as prices go, he is very reasonable.
I'm split as to which one is my favorite, the 3EB module is unique and the plexi module has great Crunch for 60's-70's pop-rock.
Sacred Groove- I have 2 base mods sitting with Scott at SG waiting for them to be turned into a Bully and Afterlife. I'd love for my mods to be finished soon, but Scott only mods modules in his spare time, so wait times are long (at least that's what I think). When I get my modules back I can better report on how I feel his work stacks up. I can however say that many people love his MK22 which is based on a Marshall JMP.
GigMods- I've never had a GM module. Pete was one of the first guys to start modding MTS modules. While he doesn't modify MTS stuff anymore, his work occasionally pops up in the classifieds.
As far as how the modders stack up- I think JF and Salvo are on the same level. They each do things differently and very well. . If you want one great tone, with less tweakability, check out what Trace @ voodoo offers. I can't yet comment on SG. Tghe only modded module I was ever disappointed with was the Friedman Brown Eye.
As for stock modules, I feel the good ones are the Lynch mods (Grail, Scary, SuperV, GTO), SL+, and Plexi. The worst stockers are the Blackface and Brown.