Zillions-of-Games values the Cannon more than the Nightrider. The main advantage of the Cannon is that it can attack other pieces without being attacked back by them. The Nightrider can do that from a distance, but up close, many pieces it attacks could capture it. Thanks to the greater power of an Eques Rex to corral the other one, a player whose only piece besides his Eques Rex is a Cannon or a Nightrider is still capable of checkmating his opponent. In the position below, the White Eques Rex covers every possible move of Black's, and White may checkmate Black by moving the Cannon to f2 or the Nightrider to j2. The only issue with this position is that it's impossible after Black's move, because Black's Eques Rex could not legally move to f10 from any space it could have legally occupied while White's Eques Rex was already on f8.
So, consider this position instead:
Here, White was able to corral Black's Eques Rex without stalemating him, because Black had another piece he could move, but that piece is unable to stop either checkmate.
Finally, this position shows how a Cannon could be better than a Nightrider in the endgame:
In this position, the Cannon's position allows White to checkmate his opponent by moving his Eques Rex to f8. I do not believe that the Nightrider offers any comparable possibility.
Zillions-of-Games values the Cannon more than the Nightrider. The main advantage of the Cannon is that it can attack other pieces without being attacked back by them. The Nightrider can do that from a distance, but up close, many pieces it attacks could capture it. Thanks to the greater power of an Eques Rex to corral the other one, a player whose only piece besides his Eques Rex is a Cannon or a Nightrider is still capable of checkmating his opponent. In the position below, the White Eques Rex covers every possible move of Black's, and White may checkmate Black by moving the Cannon to f2 or the Nightrider to j2. The only issue with this position is that it's impossible after Black's move, because Black's Eques Rex could not legally move to f10 from any space it could have legally occupied while White's Eques Rex was already on f8.
So, consider this position instead:
Here, White was able to corral Black's Eques Rex without stalemating him, because Black had another piece he could move, but that piece is unable to stop either checkmate.
Finally, this position shows how a Cannon could be better than a Nightrider in the endgame:
In this position, the Cannon's position allows White to checkmate his opponent by moving his Eques Rex to f8. I do not believe that the Nightrider offers any comparable possibility.