Flight from Pisa to USA

Should we find a hotel near the airport, or closer to the central area?
Central area.
The PSA airport is nearly walking distance from the central station (5 min by taxi or people mover). Even the tower and Duomo, aren't much farther away (add 10 min by taxi), therefore there is no reason to stay any closer to the airport. I'm not even sure there is any hotel closer.

And how convenient is public transport between the airport and the Tower area?
A taxi is best (10 min). I wouldn't bother with a city bus + people mover from the station.

I would especially appreciate a reply from folks who have flown back to the US from the Pisa Airport.
I know Pisa well enough to know just as much or more than anybody who has flown to the US from there. I have not flown back to the US from Pisa, but I don't think you will either, because Delta no longer operates its daily flight from PSA to JFK. So unless things change next year, I presume you will be on a flight to somewhere else in Europe, where you catch your plane to the US.

There is now a "people mover" train connecting Pisa Centrale station and the airport, so I see no reason to choose an airport location. There is a small train station near the tower, Pisa San Rossare, but staying in central Pisa, I imagine there is a city bus that would work better. Might not even be a bad walk.

Roberto, we are booked on a return flight from Pisa on Lufthansa; flight to Munich, and then on to San Francisco. We booked our return through United. The problem we are having is not being able to upgrade to economy plus/premium and choosing our seats.

If you booked award travel, the UA and LH systems do not integrate. You should call Lufthansa.

Call Lufthansa for the SFO-MUC-SFO portion.
Don't bother for the PSA MUC portion. The flight is short and there are no middle seats on the E195. Also no premium economy. The configuration of seats is 2+2.

If you booked award travel, the UA and LH systems do not integrate. You should call Lufthansa.

Actually, booking economy award travel on UA's website for a Lufthansa flight is one way you generally are able to get a seat reservation on Lufthansa's website any time after booking. I've been able to do this on 4/4 such reservations in the past three years. All you need to know about UA/Lufthansa and seating is available in this thread over on FlyerTalk.

Did you find your LA confirmation codes which are different from the Ua confirmation codes?
We booked ua to Frankfurt and LA to Verona. One of the tickets was with FF miles and that's the one that just handed us a seat reservation on the Lufthansa portion which we found when signing into LA website to see the reservation. The other ticket purchased at the same time but not with miles would not generate a seat assignment and LA could not reserve it over the phone when I called the first time. All UA flts sests reserved no issues including premium economy both tickets. Just the single LA ticket non ff miles portion was at issue. However I have a past history that makes flying more emotional and need to have a seat next to my support person. I explained this history briefly to LA and so far have a hold on a seat which may fall off Ibam told. I was told to call back the day before the first leg of the ticket starts to confirm the seat. It shows up as reserved but might slide off.

I appreciate the many tips and suggestions. We've been rather busy and haven't had a block of time to devote to trying to upgrade our economy seats on Lufthansa and select seats. I will report back in the next few days if we're successful or not.
I also found an old post which addresses the United/Lufthansa planes issue.