Rozier really seems to shine the most when he's the main to top-two offensive option on the floor, because he can focus on creating for himself without worrying too much about his place. However, he's not shown that he's that helpful playing with the main guys yet, especially defensively.
Strangely, Smart seems to be the opposite. He doesn't really shine the most when he's the main to top-two offensive option on the floor. However, he really shines and his value is truly apparent when he plays with the main guys and he's the third or fourth guy where he can really focus on doing pretty much everything outside of scoring in bunches.
When it comes to trading one of them, it ultimately depends on where you see the remaining guy playing.