I am partially biased because I have seen well enough of SMS exposing himself in NT. He is 24 and has been playing for Lazio for 4 years now, in terms of mentality it doesn't get more autopilot than that. Not going to contend for scudetto in a hundred years, but also not going to relegate. Every year CL is the goal but at the same time nobody scolds you or gives you the stink eye if you fail to qualify because everyone knows that there are objectively better clubs that meet the quota so you can't be blamed.
As a player he has pretty decent footballing qualities but his mentality and heart are garbage. The guy and his manager (one Mateja Kezman) are a pair of mercenaries only looking for the highest bid and salary, so don't be fooled. If he stays at Lazio after this mercato this just confirms what I'm saying even more, someone with a burning itch to win and compete will force a move one way or another.
Between him and Dybala I would go for Dybala anytime, and that's knowing that the little twink has his own fair share of flaws as well.