Wow... you named quite a few decent tube amps. However, their sonic signatures are all over the board. From my experience, the amps such as the ARC & BAT have a much more "solid state" or analytical sound. While others mentioned, such as the Cary and some of the CJ gear (not personaly familiar with the model you mentioned) tend to be "classic tube sound" where they tend to be a bit more euphonic (phenominal mids) however not the bass control I would care for personally. I have owned Sonic Frontiers SFS-80, Music Reference RM-9 ( auditioned the RM-200 ), Cary SLM-100's, auditioned the Rogue M-150's & Zeus, as well as the Quicksilver V4's. In the middle of the amps you mentioned I would rank the Music Reference RM-200, then the VTL, then the Quicksilver V4's in the middle of the pack, with the Music Ref tending toward the analytical side, and the Quicksilver being the "warmest of the bunch" in the mids. The Berning ZH-270 I have not personally had the chance to audition, however have heard great things about it. With a 10" woofer, however I have also heard OTL amps don't have very good bottom end control, so make sure you account for speaker matching. From your criteria of "musical amp, great midrange, great soundstage,and decent bass control for a 10" woofer." You also mention amps easy to live with, bias, easy to repair, easy to find tubes, and resell. Out of all of these considerations of the amps you list, I would consider the Quicksilver V4's, the Music Reference, and then the VTL's as for personal preference. My reasoning. The sound first and foremost with all... I tend to like a nice "tube" midrange, with the best bottom end control and extension possible in both extremes on a tube amp. The quicksilver V4's allow for awesome build quality in monoblocks for a phenominal price (lack of advertising & playing the audiophile game). The Quicksilver is point to point wired, built in bias meter, and uses any output tube under the sun. I have heard it with KT-90's and each mono block was putting out 180 watts per channel. They key with a good tube amp in my mind is also being able to tube roll, and fine tune the "smallest details" of tube sonics to your preference. With the V4's you can run EL34, KT-90, KT-88, 6L6, 6550, etc, etc. Not to mention all the variations. The 180 wpc will also control your bass the best of the group. My second favorite was the RM-200. Now at the same retail price as the V4's (perhaps it was $500 less) you get half the power, and two output tubes per channel. It is also easy to bias, can use a plethora of tubes, and is built like a tank. However, in the past while biasing my RM-9 (may not be the case with RM-200 - can't recall) it was noisy and made popping sounds. It also did not have the ultimate control in the bottom end, and was not quite as open with the soundstage as the Quicksilver. The VTL would be the last of my 3 favorites in the group. It does what it is meant to do well. You hook it up, plug it in, and treat it as a solid state. NO tube rolling... well sure I guess you can, but I am told it will void your warranty. The VTL is also sent with 6550's which I personally have always found to be a bit on the dark side compared to KT-88 or KT-90's. However, the amp has good midrange, decent control of the bottom end, and is well built, probably the least best of the three but still good. Another consideration some may take into account this day and age, they are all American made. There are many out there that will make provide you with extremely satisfying sonic results. However I know for a fact, the ones that sound the best, have the most tube "flexibility" (in rolling), built like a tank, Made in the USA, great customer service are all important factors to me.
By the way in the past I have had a tube blow in both Music Reference as well as Sonic Frontiers SFS-80 and had to take both to get repaired from blowing out a cap or resistor. That will not happen with the Quicksilver... FWIW
Best of luck!
