Brown and Smack simply don’t play the same role.
Brown is a hard running link up player with height that he often doesn’t use. He’s very versatile and can be used in most positions but can’t ruck.
Smack on the other hand is an aggressive high marking player who can bring the ball to ground as well as providing a strong presence and providing an outlet for kicks down to the wings
The decision on selection will more likely come down to team balance. I personally would prefer Smack to play as a relief ruck with Brown on the interchange relieving both forward and back.
But as much as I like what Brown brings to the table if it came down to a choice between the two of them I would choose Smack because I think he provides something that the team needs more.
It was probably the best 4 quarter game I saw him play yesterday, every time it was kicked to him he either marked it or brought it to ground and often either got the crumbs or fed it to a team mate