Factors to Consider in Selecting a Tube Amp

[Amadave]

I am wanting to go to a tube amp in my system. I asked 2 dealers for their recommendations. Currently, I have Rockport Atrias and both dealers were aware of this when proposing recommendations. I asked them to provide a recommendation for each tube amp brand they carried. The recommendations were:

Audio Research 150SE
VTL S-200
Mcintosh (2) MC75 monos
BAT VK-55SE

I have heard the BAT with speakers and liked the sound. The BAT is only 55 watts per channel. Aside from the Mcintosh at 75 watts, the others are much higher. Is there a reason why there would be so much variation in the power between brands? For what it’s worth, my room is relatively small and I don’t typically listen at high volumes.