Since this is a cap world, you'd have to see what those Free Agents would be asking for...
Dorsett is contracted at $2M next season (which happens to be his contract year)
Boyle is due a raise, probably around $2M
Moore is due a small raise, most likely to $1.3-1.45
Carcillo may only be due his his maximum salary as an NHL player of $1.045M...
So, 4 4th liners for 3 spots...
You keep Moore and Carcillo. Then it becomes between Dorsett and Boyle... That breaks down to two things:
Dorsett is the more offensive player of the two, who can actually fight, skate decently, kill penalties, etc
Boyle is the more defensive player, who excels at faceoffs, defensive zone play, and heart and soul...
It's a toss up. The only thing is that ONE of these guys can (and probably should) be traded for a draft pick, so who knows..