I actually think this depends on what happens to these two before the season starts. There are a whole lot of scenarios where we trade at least one of these two. Whoever stays will probably lose minutes to better players. It's even possible that Ainge pulls off a blockbuster, and whoever is left gets a big opportunity. I do think it is very unlikely both of these guys keep their current roles intact.
That being said, I vote for Rozier, especially if we draft a point guard. I don't know if Marcus has the talent to fix his flaws. I have little doubt that Rozier will develop into a very useful two way player.