Classic BAT vs. Audio Research

The house sound from BAT tends to be a bit darker than ARC. The criticism of BAT is that it's a bit on the dark side. Criticism of ARC is it's not "tubey" enough. I happen to disagree with both criticisms. I'm a big ARC amp fan, especially over the last 5 years or so starting with the Ref 150 amp. On the other hand, I have not not heard a BAT product that I did find alluring with a dash of that darkness that can sound seductive. Both companies stand behind their product. You can't go wrong. 
But as for the Ref 150se or GS 150, these are the 2 best amps in that power range that I have ever heard. These are very special amps.

Hi imgoodwithtools
If you’ve got the dough, go Ref 150 se or GS 150. I have a Ref 150 which I purchased when it came out. I later dropped KT 150s from ARC into the unit to obtain what I have been told by ARC insiders gets me 90% of the way to a Ref 150 se. The Kt 150s were a noticeable improvement but not as noticeable as when I went from my Ref 110 to my Ref 150 which was huge. If I were buying from scratch, I’d buy the GS 150 or Ref 150se. I believe some members here have compared the 2 and preferred the GS 150 by a slight margin. Scroll around and I’m sure you’ll find those comparisons.
OTOH, the Ref 150 is a great amp with KT 120s. If the price is right, consider purchasing the unit with KT 120s and  and replacing them with KT 150s in the future so the cost can be spread out. I assure you that all of the above options will provide you with great satisfaction.