What is best? I have no idea. I can say this, I have a Two Rock Custom that sounds pretty freaking incredible with the wife and child updstairs awake, but not disturbed by the volume levels. For wife and child asleep, it is workable but it does lose its magic at that low a volume.
Nowadays, many of the better amps have great Master Volumes (or other form of attenuation). - Two Rock, VHT, Fuchs, Aiken, THD, etc.
You need to figure out what style amp you want, then you can find one with a great low volume sound.
All of the Two Rocks I've owned had exceptional master volumes. So do my SLO and Makoplex. The best MV I've ever used though is on my Uberschall. Incredibly huge tone that can go from crushing to fat and woody at any volume.
The one high gain amp whose MV disappointed me was a Splawn Quickrod. It needed some volume to open up.
+1!! I've owned a lot of master volume amps, and the Uberschall by far was the best at sounding great at any volume. In contrast, I thought the Shiva needed to be really opened up to sound good whereas the 100B and 101B was good, but not great in terms of having a good master volume. Mark Cameron's Aldrich mod also sounds killer at any volume too.
Admittedly I haven't used the other amps mentioned so far, but the Guytron I'm using has a slaved power amp section for real power tube OD before the MV, so it is designed around the idea of getting true amp overdrive at any volume. The limiting factor is driving speakers hard enough to contribute to the quality of the OD, but that is true with any amp.
+1 for Power scaling. It can be installed on any tube amplifier. I played a 100 watt marshall that was power scaled at television volume and got a great cranked tone. Master volume does not even come close. I have seen it installed on supers, bassmans, marshalls, boogies. Works awesome. I am sold on it.