KPRF is the old-school Marxist-Leninist communist party and the one which is most principled anti-imperialist. It's also by far the biggest one, in fact it's the second biggest political force in Russia behind Putin's liberal United Russia party.
The other "communist parties" that exist in Russia are insignificant fringe groups of Trotskyists and ultra-leftists who hate Putin so much that they would rather side with the imperialists and help them destroy Russia thinking they can do another revolution after this government is toppled kind of like Trotskyists thought that they could have a second revolution if Stalin was defeated by the Nazis. It is no coincidence that some of them are outright funded by the West...