Bryston 4B3 or Ps Audio M700 monoblock?

About 4 months ago, I replaced my classic Adcom 555-II amp with the PS Audio M700 mono blocks, and I have been very pleased with the upgrade in sound. The M700s are very clear, dynamic, and musical while running cool and not requiring a strong back to move them. Stereophile calls them "an outstanding bargain," and I enthusiastically agree. 

I am sure that the Bryston 4B3 is a strong performer, but it is also significantly more expensive than the M700 pair. I have not heard the Parasound A21+, but it would have been my second choice when I bought the M700s. The issues that drew me toward the M700s (in addition to the great reviews) were the fantastic discount available if you have any gear to trade in and the 30-day in-home trial from PS Audio. If you want to demo the M700s before you confirm your purchase, you can try them in your system and see if they create any magic with your gear. If they don't, just send them back. 

Good luck with your search for a new power amp!

For those who don't know a lot about the Stellar M700 monoblock, It was designed by a passionate young engineer named Darren Myers, who is also a committed audiophile. He worked for Classe and B&W before being hired by PS Audio. His excitement in designing gear that sounds really good is shown clearly in a YouTube video of an interview he did at AXPONA 2019 with Michael Fremer: https://www.youtube.com/watch?v=oFspgDyjEQo

I had already bought my M700s by the time I saw this video, but it was fun to find out a bit more about the main engineer behind the PS Audio Stellar gear.