What's Best , Audio Research VT-100 or VT-100 MKII

I use to own the MK I. It has a laid back soft around the edges kind of sound and you'll need to drive it up a bit to get the sweet characteristics. All in all this is a very nice sounding amp.

I now own the MK III which sounds completely different than the MK I so much so that it's kind of hard to compare the two. They’re two entirely different sounding pieces.

As for the MK II I have no idea but many reviews seem to indicate that they sound slightly better than the MK I.

I've never heard of anyone who was sorry that they upgraded a MKI to a MKII. If you're referring to the upgrade from MKII to MKIII, I attended an A/B comparison between them in a highly tweaked system. The clear concensus was that the MKIII is more resolving -- there's more detail (which is saying a lot, as the MKII is no slouch), but the highs seem a bit accentuated compared to a MKII, which can make the amp sound a bit bright. On perfect material, it's a better amp, but the MKII is definitely easier on the ears and will do a better job with less-than-perfect recordings (most of my collection). Three of the attendees (including myself) have MKIIs, and I don't think any of us intend to upgrade. Hope this helps.

I agree with Larryro -- never have I heard anyone say the Mk I was better than the Mk II. It is the opposite -- the Mk II is more powerful with a beefier power supply, a cooling fan, and some circuit changes. It would be more accurate to say that many people prefer the Mk II to either the Mk I or the Mk III. More than once I have heard the Mk III described as Larryro describes it -- perhaps even more resolving than the Mk II, but at a price in the highs. I had a VT-100 Mk II for sale, but changed my mind and kept it. It sounds great.