Car rental on Paros

It appears the choices are Enterprise, Sixt and Europcar.

If I were choosing, I would look at Enterprise 1st, because of their having a US base. It may make it easier to contact if there are any after the trip "issues"

I have heard of the others but never used them. The only occasion I had to rent a car outside the US , I got a car from Hertz.

It was so long ago that we rented a car on Paros that I can't even remember the rental company. However having said that we have rented cars in Greece for many trips. For an island like Paros in the shoulderish season there is no need to rent in advance. We choose a day that makes sense for us and the night before we visit several rental agencies to get the best price and car option.
We sign the rental agreement and pick up the car the next day. Parking in the towns can be difficult so we return the car that evening so we don't have to deal with parking.
All that to say there will be lots of choices when you arrive. We avoid the big brand name rental agencies and instead concentrate on locally owned rental companies that offer full insurance coverage with no deductibles. Local companies will work hard for your business.

I agree with Stan -- arrange your car the night before, pick it up in the morning and return at the end of the day.

With 5 days, you might want to spend one day on the water, and I highly recommend a "Lazy Day with Captain Ben." This is a full-day boat trip around Antiparos including lunch and drinks. He's based in Antiparos but makes the short trip to Pounda to pick up Paros passengers. He may not go out every day in September, so you might want to contact him before you leave or shortly upon arriving, to get a spot on his boat. It's a great way to spend a day.

Thank you all for your replies.
Stan, I have enjoyed looking at your photos, on this site and another.