Soldano and THD are the only production amps I've ever seen that rival Mesa for build quality.
In terms of transformers, they kill Mesa. You just can't beat Mercury Magnetics. They are easily twice the size/weight of the Mesa transformers.
Based on my needs for a really great clean tone, great Reverb and thick distortion that really sings, I would recommend:
Choice 1:
Soldano Lucky 13 (just needs a couple of simple mods to sound extremely close to the SLO.
Reverb is a little noisy, but extremely lush and deep.
Clean channel is the best non-Fender clean I've ever used, hands down.
The distortion channel does need a mod to get high enough gain to satisfy me, and there is no FX Loop.
But....The mods are easy and with the proper Loop circuit, this is the ultimate amp in my opinion. Built like a Russian wife, as simple to operate as a pay phone, Distortion that will send almost any other amp running for cover, and a clean sound that is sweeter than Jessica Alba!
These are the under dogs of the Soldano world because they do not come from the factory with the SLO gain.
Choice 2:
Heartbreaker.
With a Reverb mod and a high gain mod on channel 2, you can get Twin Reverb clang and some seriously sweet Marshall-esque distortion without the crappy Marshall build quality!
The Loop is very transparent.
Cleans are incredibly sweet!
Solo Boost can be added as well, making this amp much more versatile than the Lucky 13.
Lots of options too!!!!
Not nearly as much distortion as the Recto or SLO though unless you get it seriously modded.
Choice 3:
Mesa DC-10.
Reverb can be great with a simple mod.
Loop can be great with a simple mod.
Cleans are very sweet and articulate with nice warmth.
Distortion tones are over the top, but not quite Recto or SLO.
The EQ really adds to the versatility though.
I haven't had the chance to try a Knucklehead yet. The nearest Rivera dealer is over 200 miles away.
Who am I kidding, the nearest music store that doesn't suck dog balls is over 200 miles away! But, I have over 20 trees in my yard and the air is clean!
I haven't tried an Avenger yet either. To be honest, it doesn't hold my interest. I did have a Hot Rod 100+ (the channel switching model). It was ok, but I had the Lucky 13 at the same time and it absolutely blew the HR away!
Soldano is more into the stripped down, hot-rodded theory of amps. He doesn't want to put a bunch of useless or confusing options. He is concentrating more on the purest tone he can get out of his amps. That says a lot in todays world of 1000's of options and choices.