Upsides are close but the downside is that Clarkson could go back to being goal-heavy with a lack of assists making him a points-only bust. Go with Kunitz.
Kunitz is the safer option as he's already reached 60 points in a season. Clarkson is averaging over 4 shots a game though, so he's definitely stepping up his offensive game. I would guess they will be pretty close in points by the end of the year. I would go for Kunitz because he's the safer option, but you may be able to get an even better return... Maybe somebody with a slow start like Eriksson?