To be honest I think it’d be cool if trump waited until after the election. Just to get people motivated to go out and vote for him.
Kind of like if you believe your gonna win then “put your justice nominee where your mouth is” 
Edit: might also go over really well with independents and undecided voters.
That's one strategy.
Even if Trump makes his pick now, the Senate still has to confirm. Look at how long the Dems drug out the Kavanaugh hearings, trying to delay it until after the midterms. Had the Dems won the Senate, they could have blocked Kavanaugh's confirmation. That cluster was the worst circus in the history of Congress.
If that crap happens again, Trump can use the circus/hearings to fire up his voting base. He won't have to delay his nomination until after the election, because the Dems will try to do that for him.
I'm not sure what the rules are, but once a nomination is before the Senate, I would think the Senate has to vote for confirmation at some point. Could a President Biden (

) withdraw a SC nomination once it's presented to the Senate for confirmation? Would be interesting to see him try.
I think Trump should go ahead with the nomination. If confirmation happens, that's a very good thing whether Trump wins reelection or not. Plus, I don't believe Biden is going to win. Even if he survives the debates, I think any enthusiasm for him will fade once his lack of faculties is demonstrated for all to see.
If Trump wins, there's the probability the Dems/Leftist groups will contest the election results again, riot and drag the final electoral vote out as long as possible, which could delay the SC nomination.
Better to get this SC pick in the "win" column as soon as possible, while the Dems are more focused on stealing the election.
I heard Adam Schiff has another whistleblower report and is opening another investigation into Trump. That man has no credibility, but it isn't stopping him. I guess he figures his image can't get any worse!

That could easily be the Dem's "October Surprise" for 2020.
All that on top of what punaperson said re: a missing jurist on the court for that long.
The sooner, the better.