Ps Audio BHK Signature vs Parasound Halo A 21+

There is more to amplifier design that the kind of output transistor used and the choice is up to the designer.  And not all speakers are in the same difficult to drive category as Wilsons.  Hell my old JVC boom box uses bipolars   but it doesn't compare to my Pass amp.
 

Your question is impossible for any of us to answer reasonably. The better amp is the one that sounds better to YOU, with your system in your room. None of us can predict that.

altchavez OP
Thanks , my speakers are a pair of Dynaudio Contour 20

These shouldn’t be a problem not too hard to drive with either Bi-Polar or Mosfet amps even Class-D or Tube, in either reflex (ported) or infinite-baffle modes
https://www.stereophile.com/images/417DC20fig1.jpg

https://www.stereophile.com/images/417DC20fig2.jpg

Though there is a combination of 5.2 ohms and –38° capacitive phase angle at 120Hz, the Contour 20 will work well with tube amplifiers, as Herb found.

Cheers George

There is more to amplifier design that the kind of output transistor used

Read everything, that why this is said at the end.

  So to me it comes down to what speaker you have, and if they are easy load and suits both amps, then try to listen to both on your speakers, and pick the one that sounds better.

MOSFET amplifiers can be very capable of providing adequate current.  The Audio by Van Alstine FET Valve 600R I have drives my Magneplanar 3.7i's very well.  Certainly as well as my Parasound Halo A21 from the listening perspective.  According to its specifications, the BHK doubles its 8 ohm output into 4 ohms.  Don't know how that can be done without increasing current commensurately.  But I'm certainly willing to be educated.