Realize you need to make reservations well in advance. Any recommendations for either island appreciated.

It has been a couple of years so someone else may have more recent information but we rented a jeep for the week from Carlos Jeep Rentals on Culebra. They were nice to deal with and the jeep was new and clean- no problems. I would recommend them or use them again.

I use Martineau Bay Car rental on Vieques and have been very pleased

I've used Allen Thompson with Vieques Car Rental. We did have a problem with one of the windows getting stuck on a newer jeep... mosquitoes were enjoying themselves!
Allen replaced the car with an older version for the rest of our stay and gave us a rebate (as the car was older).

I used Martineau's on Vieques and was very pleased with the experience. We received a new Jeep and the check in/check out process went quickly. Be sure to walk around and notate any damage before driving away. We received a few branch scratches from going to the remote beaches and they were not concerned when we returning it.