which is better, a car or train from Naples south to Serra San Bruno (SE of Pizzo)

You will find no rental cars in Pizzo. But if you want to avoid the long drive from Naples, take the train to LAMEZIA TERME CENTRALE.
You could also fly to LAMEZIA CENTRALE from Rome, unless you are in Naples for other reasons.
Next to the Lamezia Terme Centrale station or also at the nearby airport, you will find all major rental companies.
The drive from Lamezia T. to Serra San Bruno is just a bit over one hour.
For train schedules see:
www.trenitalia.com
If you want to fly there directly from Rome or elsewhere (I don’t think there are flight from Naples, since it’s not that far) the Lamezia Terme Airport code is SUF (the district the airport is located is actually called Santa Eufemia)
To rent cars in Italy I use a broker called www.autoeurope.com, I highly recommend it.
Avis and Hertz (and others) are located next to the Lamezia Terme Centrale station. The airport is also not far from the station.all major companies are at the airport also.
Buon viaggio.

One issue in renting a car in Italy is that many tourists wind up with expensive tickets in the mail months after they return home.
There are many rules about having permission to enter many Italian towns and cities; driving in the wrong lane (bus lane for example); and getting a ticket because of a speed camera (I got a ticket in England going 35 mph in a 30 mph zone for 40 GBP.

Also, trains seem to go everywhere in Italy.

https://www.autoeurope.eu/travel-blog/what-are-ztl-zones-in-italy/

https://en.wikipedia.org/wiki/Road_signs_in_Italy

Both GoogleMaps and Waze have a Speed camera alert option, however in my experience Waze is better at detecting all.
https://support.google.com/waze/answer/15758855?hl=en

If you want to go to Serra San Bruno unfortunately a rental car is a must. Many small towns in Italy are on top of hills and/or in very mountainous areas where trains can’t go. There are buses of course, but service may not be frequent.

Thank you for the helpful information. I really wasn't looking forward to long drive, as I would rather take in the countryside we pass thru rather than have to concentrate on driving in a foreign country. I'll check for available trains to Lamezia Terme.

You'll be on the freeway for half the way.
I suggest you stay on the A2 freeway (Salerno-Reggio Calabria, aka SA-RC, or also Autostrada del Mediterraneo) and I suggest you exit at the VAZZANO exit.
From there go toward Vazzano, the from Vazzano go toward Vallelonga, and finally to Sierra San Bruno.
This route to Serra San Bruno is a bit longer, but not as narrow and scary like the others suggested by GoogleMaps. Sometimes navigators send you into some strange country roads which are paved but very narrow (like two lanes as wide as one lane).

Thanks again for the added tips on driving. Much appreciated!