I'm going to say Rozier - I think he has much higher upside and has the potential to become a dominant scorer and a star.
I don't see that with Portis.
As with the draft, I always select the best player available - I think Rozier is a better player then Portis, and I think he'd see that if he got more opportunity.
Rozier got called up in the playoffs as a ~20 year old rookie who had barely played 48 minutes of NBA basketball, and he made legit contributions on the biggest stage. I can't stress enough how difficult it would be to produce in the playoffs after not playing all season - even for a veteran. For a rookie to be able to step up and do that is huge - it speaks volumes of Rozier's character, his confidence and his talent.
He's going to be a special player.
I feel like you're making a huge reach here. But assuming you're right, why have we not already traded Smart to upgrade the frontcourt?
For a couple of reasons.
1) With Turner gone, Rozier and Smart are the quality guards we have on our bench. Trade out Smart and you leave Rozier as our only guard off the bench. It's very risky. If Rozier gets hurt (Knock on wood) we would have to depend on unproven rookies and scrubs (Jackson, Hunter, Young) to play significant minutes, and that's too risky on a team that has playoff aspirations.
2) I would hazard a a guess that right now, Smart's value on the trade market is probably not especially high. He's essentially a one dimensional player - a defensive minded PG who is a poor shooter, a poor scorer, and an average playmaker. He also has relatively limited upside. There's no point in trading Smart and breaking up our back-court unless it could get us the type of big who could make a major impact. There is no evidence thus far to suggest Smart has enough trade value to be able to pull in a frontcourt player of that caliber.
3) Rozier has shown us some of his capabilities, but he's still a young player with very little experience. He's a clear cut above everybody else on the summer league team, as he should be, but it still might take another 6 months or even another year before he has enough experience to be able to contribute
consistently at the NBA level. Remember that Sully and Olynyk were both nearly useless until about half way through their rookie years, and they were getting a consistent 10-20 minutes of playing time every night. Rozier has maybe 10 games of signifiicant NBA experience, and as a PG his position is a trickier one to learn. I've got no doubts that he will be a better player then Smart in time, but he does need time.
Smart has his limitations, but he's got almost two complete seasons of experience under his belt and he can lead that second unit.
If Boston could pull off a trade for a good big man and also get a decent backup guard in that deal to go with it, then I don't think he'd hesitate to trade Smart. If he could get a star big man (e.g. Cousins) then I don't think he'd hesitate regardless.
Remember, I just said that Rozier is going to be a special player - I didn't say that it's going to happen overnight.
When it comes to the frontcourt, I honestly have a sneaking suspicion that Sully will be back - even if just on a one year deal. We need a big man who can be depended on as a starter, and as much as i do not like Sully he's the closest we have to a starting caliber big right now. Horford can cover a lot of his flaws, and Sully is actually a pretty good player so long as he's not being asked to do too much. I don't think Danny wants to do it, and if he can find a better big (Okafor, Noel, Cousins) without sacrificing too much, I have no doubt he'll do it. But if he can't make one of those deals happen then one more year of Sully is probably the best bet. In that case we will have Amir, Olynyk, Jerebko, Brown, Smart and Rozier off the bench. I'm not even sure if that is enough veteran leadership to be honest...losing Turner has really hurt us.