No personal experience with the Campania Express train but it's not as busy as the Circ., has air conditioning, and is reported to be more comfortable overall. The drawback is that it has far, far fewer daily runs than the Circumvesuviana - only 4 from Garibaldi - so there's quite a gap between trains.
https://www.sorrentoinsider.com/en/campania-express-train-schedule
The drawback for the ferry is that it involves a transfer from Centrale to the port, and then another transfer in Sorrento from marina up to the main part of the town (if that's where you're staying). It's also no fun in rain: been there; done that.
https://www.sorrentoinsider.com/en/ferry-schedule?from=napoli&to=sorrento#
(this is the current winter schedule)
While the Circ is a battered, no-frills thing, it has frequent departures from a station (Garibaldi) connected to Napoli Centrale, where your train will arrive from Rome. It's also very inexpensive. Trains arrive in the main, upper part of Sorrento possibly within walking distance of your accommodation, as was true for us.
Current Circ. schedule:
https://www.sorrentoinsider.com/en/naples-to-sorrento-train-schedule