I don't want to overstate the case, but there is a certain ... wild-west ... aspect to life in Naples, so I think good references are very important in your choice. If you are using a full-size, "real" hotel, it is almost certain that they have a "land partner" for car services. They have guests who need transportation to the Amalifi Coast or Sorrento or Caserta all the time, and they don't (probably) run a car business themselves. That's what we did with our Sorrento stay. However, we only used a car to return to Naples, we took the gritty Circumvesuviana on the way into Sorrento.
My point is that this is a long-term relationship that is vetted by the hotel. The partner has a huge incentive to provide good service at a competitive price. I don't mean "wild-west" to sound scary. It's more that you have to carry a printout of the Flat Rate taxi rules to show to the airport cab who tries to charge you a variable-rate, or charge for each suitcase!
Not that it's crucial, but we charged our two car service jobs from Sorrento to our Ambasciatori hotel bill, which was convenient. (A very big hotel, owned in a group with other big hotels. Our one night in Naples was a tiny place. I wish we'd had more time in Naples.)
Edit: It's important not to assume that a competent, gracious driver is also a qualified "guide." I mention that after remembering some posters here have noted that it's important to prepare for a "roots" visit to get the most out of it; church hours, town hall policies, records in Italian, possible local names. You can't expect to have a TV program-experience if you just show up, I mean. No personal experience.