According to Fedor a lot of NBA folks view Mobley as more of an Anthony Davis than as a center.
At 6'7" and not much of a rebounder, Larry Nance, Jr is more of a defensive and passing-minded 3 than a 4. Fedor also said some in the Cavs organization view Okoro as a better 2 than a 3.
If we can get Mobley I see a domino effect where Mobley takes over at the 4 (the Cavs plan to reduce Love's minutes), which pushes Nance to the 3 and Okoro into a rotation of Sexton, Garland, and Okoro at guard.
The Cavs did well last year with Dante Exum at the 2 before he was injured. Okoro has a similar game to Exum but with more upside.
Right now I believe both Nance and Okoro are not playing their strongest positions and would benefit from moving to small forward and shooting guard, respectively. Getting Mobley would have a ripple effect that would improve three positions IMO.
Green would be great because the Cavs were 28th in points per possession last year and Green is a scorer. Mobley is more like a bigger Okoro - great defensively but not a guy who can create his own shot at this point. Allen is also not a shot creator so putting Allen, Mobley, and either Nance or Okoro on the front line together would put tremendous pressure on the guards to break down the defense and get open shots for these guys. That's what Garland and Sexton do, but they wouldn't be able to take any possessions off.
Between Green and Mobley there's no wrong answer, but neither is the perfect answer, either. But I think getting an elite wing defender in Mobley while adding size and length, plus being able to put both Nance and Okoro at their best positions would be more helpful then just getting a talented shooting guard. However, it's not like the Cavs will have a choice - it's entirely up to the Rockets.