Vucevic.
Grant is having his first season of being anything besides a nice role player, and it happens to be on the team where he's option #1 for the first time. He'd quickly look like a bad investment given he'd be the 4th option here, and would look like Denver Grant. Plus, he left to go be "the guy".
Vucevic, since 2014, has averaged 19/11/3, and has over the last couple of years improved his shooting and passing to where he is now a deadly 3 point shooter. He'd also be a similar high-post passing presence to Horford, something this offence is crying out for. I'd want us to ship out Thompson as well as maybe Theis though, because our current big rotation is actually solid with the ascendancy of TimeLord. Even with that, I would prefer the borderline All-NBA calibre big over the fringe All-Star wing