I'm more of a Marshall tone fan, I've owned a Recto Head, a Mark IV, a Soldano, and quite a few Marshalls (nothing newer than an old EL-34 JCM900), I've also played a Bogner Ecstacy
(wish I could afford one). I have to admit, I'm not a fan of Rectos or Mark IVs, they have nice rhythm sounds and the clean on the Mark IV was great, but I didn't like the lead tones, they tend to get lost. The high end is "thin" on the Rectos, and the Mark IV (for me, I know there are a lot of fans here) didn't have the harmonic content of a good Marshall type amp. My favorite amp that I've had was a Soldano HR50+, great sounding amp. I also like a head and 2-12 cab (don't have much use for hauling 4-12s at the moment) better than combos. I also think they are easier to move around, sure it's 2 pieces, but easier to carry one in each hand than a heavy combo. I also like the closed back sound.
Sorry about digressing OT, the Shiva is a stripped down Ecstacy, with a few other goodies, like the Schizo switch. I've heard them and they sound great, personally I would try to get an EL-34 version, again, that's the Marshall lover in me.
Hope this helps, but most important is that it sounds good to you, there are some great sounding recordings done with Mesas, they just don't seem to cut if for me.
Edit: I just looked up the Bogner site, the Shiva doesn't have the Schizo swith, that was on the Caveman which is discontinued, the Shiva has a boost function. Still a great amp! There are lots of sound files at www.bogneramplification.com