Haywood, who is Saints’ top try scorer this season, has played the majority of games at hooker, with Hartley away with England having been hit with a six-week ban in December.
But Hartley has started Saints’ past two matches since returning from leading England to the Six Nations title.
And West says there is little between the two men as both seek the starting shirt at Franklin’s Gardens.
“Dylan’s come back into the side and it’s really close in terms of who we pick between him and Mikey,” West said.
“They’ve got variation in what they can do so we’ve got some good options there with the two hookers and we’re really pleased with how they’re playing.
“Dylan’s always had a full 80 in him but you’d struggle to see any hooker go through a full match because you’ve usually got a quality player on the bench and you look to freshen things up.
“It’s such an integral position that the fresher the player is, the better, and I’m sure every club picks their team with that in mind.
“You know you can bring someone like Mikey Haywood onto the pitch and he’ll add to the game.
“It’s no different with England, who have got players like Jamie George to come on and make an impact.”