Hey Jetter,
When Nelson Pass has been asked what is his all time favorite amplifier that he created/designed he says all of them!
As I stated it's my personal favorite of the .8 generation of amplifiers. However, I have a soft spot in my audiophile heart for the Threshold SA-1 mono-blocks because they too were warm,full, and sweet sounding but with great dynamics.
I forget to mention I also own a First Watt SIT2 that's also a wonderful music maker. Each of Nelson's creations offer slightly different "flavors" and the matching of the amps with the right speaker load also is very important. I loved the XA-25 on Tekton Double Impacts-pure magic, but found that my much larger 21 driver ULf's, that are easy to drive but love high current, did not match up as well with the XA-25 that's were the X-250.8 sounded better.
So, it's not the amplifier in isolation, but the matching/synergy to different speaker loads that tells the tail of the sonic tape. Still, the XA-25, with the right speakers is a "gem" of an amplifier at a reasonable price.