Best way to compare amps?

If you have some extra speakers and cables, then leave the other amp turned on in another room, so it is warm when you make the switch. A cold amp is going to give you a bad first impression against the other one. Many amps take a couple hours to get up to speed from a cold start.

I am guessing that part of the reason Sean above did not think the Mission was better at first is because of a cold amp (and switching back to the NAD).

You maybe can just leave the other amp on with nothing connected to it, but I am never sure if this is good for the amp.

I would suggest listen to them for a couple of weeks ea. minimum because you have to both let it run in with your system & also audition under varying circumstances which include different times of the day. Also you might want to experiment with/without power conditioners & PC's if you have them. Good luck & let us know your results!

An interesting observation that I've noticed when A/B 'ing ALL TYPES of audio gear. (Seantaylor99 alluded to this fact!) Sometimes, It's tough to notice an improvement in audio quality. But when going back to a lesser sounding piece of gear, the difference in lower audio quality jumps out quite clearly! Seems that most people find it easier to hear a degradation in audio quality than an improvement! Happy Tunes!

What Fatparrot is saying was my experience with power conditioners and speaker cables. May help explain why some claim they make no difference at all. They plugged in the conditioner or new cables, heard no big immediate difference and gave up. I also had the same experience with my REL sub. When I shut is off after having it for a while, I thought: "Where did the music go?"

Sugarbrie ... I don't think warmup was the reason. Warmup may make something of a difference bu nothing as profound as what I heard. I think fatparrot is close to my experience. You may not notice the step up, but boy do you ever notice the step down. This applies to many other areas of life too.