Neither. ugh. If those are the choices available, save the money for 2017. No need to blow our space on mediocrity and bad fits now.
Parsons is bigger, a better shooter, a better defender. Derozan is quicker, a better shot-creator, and draws a lot more fouls/free throws. I see Derozan as a primary scorer, effective with the ball in his hands; whereas Parsons is more of a supporting player who can contribute in other ways. Basically, I think Parsons' skill set fits better with what we need to supplement Dame/CJ.
Both of these guys are better than "mediocrity" and would by far be our third best player. Non blazer fans would argue at least derozan is better than McCollum too. My choice is parsons.
It's refreshing that you guys don't seem to get hung up on money in these discussions. Raptors fans are biting their nails about giving DeRozan $25MM/year.