They're all good options as far as the modules go. Everything is compatible with each other. It mainly depends on what flavor you want. The main difference being that Synergy is 2 channel and Salvation/Jaded Faith are typically modded 1 channel Randall modules. Though the 2 channel Eganater modules can be modded and salvation has recently started doing some mods to the Synergy SLO modules.
If you're going for docks it's better to get the Synergy SYN 1/2 over the older Randall RM4. For heads It's a toss up. A modded Randall RM100/50 head (or modded combo amp) in my opinion is the best option, followed by one of the synergy heads. Last on the list would be unmodded Randall stuff.
Personally I have a combo of most of the above which works perfectly. I have a Jaded Faith modded RM100, a SYN2 run through it and a combo of Synergy and Jaded Faith modded modules. Synergy Modules are IICP, Pitbull, Powerball & Savage. JF modules are a Wrecked (Trainwreck Liverpool) and JFX (Peavey JSX). All of the modules sound excellent.
I haven't tried any of the Salvation modules, but I have a couple on my list. I hear their modules are top notch but the wait time can be fairly long up to several months. Communication is fairly lackluster too. From personal experience, I got a quick response asking about the ordering & modding process. Then when I contacted Salvation to actually place an order I got no response at all. So... ?
As Zen Amps suggested check out Jaded Faith. Rob is great and does great work. Never thought I could get touch sensitivity from a module like I do with the Wrecked. He generally answers emails within a few hours, but at least by the next day. And turnaround time on mods is pretty quick. Mine were completed and being sent back within 2 days. He can do more than just what's listed on his site. There's a number of modules in his backlog that he can still do and can do custom requests within reason. I wouldn't doubt he could do most of what Salvation offers. You just have to ask if you have something specific in mind. I'll be sending him another 2 modules this week. One to convert to an Ampeg SVT and the other to one based off Lemmy's Murder One Marshall Superbass. I want to run those as extra channels on my Mesa Titan bass amp.
