The Dynaco that I run is a PP amp. I was led to believe the dynamics had a lot to do with transformer size; massive in the Quicksilvers very rather smaller with the Dynaco. 'Why' really doesn't matter too much, for my applications I simply prefer the sound one over the other.
I had the ST35 briefly and a friend still has the unit in mothballs. I thought it was a great amp given its affordable long lasting EL84 output tubes. I also have an Eico integrated with 7591 outputs which is darn nice as a 7591 is supposed to be like a half of a Tungsol 6550. I am rather ignorant of the possibilities for these, but I would think adding triode mode to these would give them a sound much more like the revered directly heated triode amps.
I am really interested in the VTL Tiny Triodes which ran 4 EL84 per monoblock in triode mode for a supposed 25 watts. These would be great amps and have a strong reputation. Salvatore at Supreme Recordings recommends them.
http://www.high-endaudio.com/RC-Amplifiers.html Also on this page is a reference to "Tom Evans Linear A stereo amp; 25wpc from 4 parallel EL84s per channel driven by op amps (!), .... a revolutionary amplifier."
A fun little tube the EL84.
Quicksilvers are supposed to be easy to modify with their point to point wiring.
A friend of mine runs some custom 6550 push pulls in triode mode on his quads and they can get amazingly loud in his room with only 25 watts.