Unless 2018 is a disaster for Republicans, I think this one will be very close, regardless of who wins. Scott is almost certainly the best candidate the GOP has.
There are much more statewide-electable Florida R's: Bondi, Atwater, Putnam, Jolly, Curbelo.
Bondi: I think she's joining Trump.
Atwater: Getting out of politics
Putnam: He wants to be Governor and doesn't seem to want to return to Washington
Jolly: He has burned bridges with national Republicans, otherwise he wouldn't be as bad.
Curbelo: He'd let Nelson romp to victory in the Space Coast and panhandle. If he was running for an open Rubio seat, then yes, but Nelson always overperforms in Demosaur areas and northern Floridians probably don't want the Miami machine controlling both seats.
(You also forgot T. Rooney, D. Ross, and R. DeSantis, but I doubt any of them run, and they'd still be weaker than Scott).
Scott has lots and lots of money, and a populist/outsider/business character.
Anyway, Nelso, who has always won by large margins, is only at 44%. That isn't where I'd want to be if I was a popular incumbent Senator running for a fourth term.