A night in Paestum or Salerno?

I'd probably go for Paestum. The temples can certainly be seen quickly, and you may even have time to pop into the museum.
If you don't have too much luggage, it is a short walk from the station to the site, and there are b&bs and agriturismi all around it.

The Intercity trains to Taormina don't stop in Paestum but do stop in Salerno, so Salerno might be your better choice. If you stayed in Paestum, you'd need to take a regional train either back to Salerno or south to Sapri to connect to the Intercity train. If you're OK with that extra connection, then Paestum could be a good option. In Paestum, there's a walking path between the train station and the temples. However, there's no ticket window or kiosk at the station, so you'd need to purchase your tickets elsewhere in advance.

While the town of Paestum is pretty meh, the temples are are lovely at night, beautifully lighted. But the transportation is a bit cumbersome and jet lagged you may not really appreciate the site so much so if yo7 just pushed on to Salerno, not all bad.

I think it will all depend on your timing and plans for the overnight stop. Beyond the temples (which are GREAT and BEAUTIFUL), the town is small....if you had a LOT of wandering around time (like the train to Taormina was late in the evening so you would have a lot of the day prior to departure, though I would check to see if it was available from Paestum) I would probably say Salerno.

If you are arriving in the late afternoon or evening time and the train leaves midday and your greatest desire is to explore the temple area, Paestum would work well. If you are looking to just explore to pass some enjoyable time, I would say Salerno.

And yeah, the extra connection to Paestum might just be too much....

We thoroughly enjoyed our stay at Il Granaio dei Casabella in Paestum. The hotel is a 5 minute walk to the temples and steps away from 2 excellent restaurants. The temples and museum were beautifully preserved and well worth the visit. They were spectacular to see lit up at night as well. The hotel pre-arranged for a taxi to pick us up from the train station. The hotel staff were wonderful and helpful with our every request. We also took the train (although reverse of your trip) from Catania to Paestum and really enjoyed the relaxing ride. Happy travels!

It would be very helpful if you shared your potential travel schedule — month, day of the week, and options for arrival and departure times. Also, will you be laden down with baggage, perhaps related to the wedding? In general, I would say the wonderful Paestum temples and modest-sized but excellent museum beside them, are certainly worth the time and effort, if you can have some time there. Late in the day is the best time to visit, in terms of the light. The museum displays beautiful art and artifacts from the ruins, and most special to me, shows what the temples would have looked like, back in the day, very colorful and totally unlike the grey stones of today. The museum is included in the ticket, but is closed one day a week, Monday as I remember, but confirm that. If you have considerable luggage, an option might be to stop and get a room in Salerno, close to the train station, then go without baggage to Paestum for the late afternoon and early evening, going back to Salerno for dinner and the night. That depends on schedules. I believe there are also buses between Salerno and Paestum. Happy travels, good luck with this planning, and best wishes to the happy couple.

Larry has some great ideas! I would say it definitely depends on the schedules available.