The Classe retails for over twice as much as the Parasound A21, so it should be the better amp. I'm surprised to read that it doesn't double its wattage at 4 ohms though, but being stable at 2 ohms is pretty respectable.
Further reading on the amp shows that Classe improved the amp over the years, and it's not clear which version the OP got, a more recent version does double at 4 ohms.