Allright, I wanted to know it today, drove 200KM to a shop that had them all, and tested heads for 3 hours. Here's what i think:
Diezel VH4: Very Nice. I actually don't need more than Channel 1 and 2, but 3 is still nice, 4 is too much :) It lacks character though, although it does sound good!
Soldano HR50, SLO-100: Outch! This thing cuts through !!! There's not much bass at hand, but I guess it's VERY audible in band context. Very hard and direct, very nice in its own way, but it hurts my ears, sorry. I like the gain of the amp, but it's too bright for me, even with presence down. Liked SLO100 more than the HR50. Clean is OK, but just OK.
Custom Audio Electronics 50: Nice, refined. Nice cleans, nice crunch, nice overdrive. Where does all the hype come from? I guess this is something for pros, to me this is too boring and sophisticated, I need something more agressive.
Bogner Shiva: Aaaaahhhhhhhhh, now THIS is a nice clean sound. Wooohoooo, I am not a big clean player, but almost forgot that there is another channel. This is a VERY nice clean channel, the best I heard maybe? Switch to drive and ... THANK YOU. Man this thing has balls and crunch, I LOVE IT. No matter how you dial the it, it always sounds great. Really! On V30, on Greenbacks, different but always great. The boost channel finally is pure tone and fun. I understand now what people mean if they say that this is what Marshalls are supposed to sound like.
Bogner XTC Classic: Oh-Oh .... sh... I just thought I was happy with a 2,000 EUR amp, and now I play a 4,500 EUR one and all the happiness about the Shiva is gone. FXXX. This sounds awesome. Not better than the Shiva, just 20x more different sounds !!! Awesome. Again, there is not one bad tone no matter what the settings. Modern/Vintage? No problem. Class A or A/B? No problem, just flip a switch. 50/100 Watts? Easy. And then ... this ... arghhh ...PLEXI MODE! Goodness. I'm on my knees. This is AMAZING. NOOO, I DON'T WANNA SPEND 4,500!!! This is insane !!!!
Now I don't know. The Shiva was 100% satisfaction, I could have got it and been happy for years to come. But now I tested the Classic, and that's a different animal. Like going from B- to A League.
I tend to get the Shiva, because 4,500 EUR for an amp is crazy. On the other hand I might still be GASing if I got one. Will keep you posted, but let's vote, should I get the SHIVA or THE XTC Classic?
By the way, I will sell my Engl Screamer Top with Z5 as well as my THD UniValve with many tubes and yellowjacket adapter, if you're interested ...