I owned an original SLO with no mods. Had my tech install the depth mod because it didn't have enough low end. I found that amp to be on the darker side with a super smooth top end. Great lead amp but I kept my 5150 in favor of it because it was WAY more aggressive and the cleans on the SLO weren't really any better than it. Don't really remember its mid-gain sounds, but I keep hearing people lately compare them to Marshalls and I don't remember it sounding anywhere close to a Marshall
Interestingly, the new BAD SLOs sound totally different to me. They are brighter and a lot more aggressive. Supposedly they are the same circuit, but I'm not so sure, they definitely sound significantly more modern in the clips I've heard? The Synergy SLO module I have sounds exactly like what I hear from the BAD amps, but I find its sounds just kind of boring. Nothing really exciting about it - a good sound but nothing more than several other amps out there.
The first 101b I had was a 2007 or 2008. I thought it was one of the brightest amps I've ever heard in my life. I couldn't dial out the sizzle, especially on the Red channel, it was just too much. The cleans were also similarly bright, but I was kinda into it at the time. I remember them being harsh and brittle with the wrong guitar, though.
Now I own a 2003 101b. It's a pretty dark amp, almost polar opposite of what I remember it being, and I have to put the treble and presence a lot higher up on it, but good God does it just feels good when playing it. I've heard people talk about the FEEL of an amp for years and I understood it to an extent, but this amp just responds exactly how I want it to when I play a note. The cleans are gorgeous, though not as good as the Synergy IICP module I had, and the Red channel actually gets brutal AF. In fact, the channel I don't really like much is the Blue, which is the one everyone seems to praise. Definitely gotta spend more time there.