You will be able to rent wave runners at most of the public beaches along the hotel zones at these ports.
In Aruba, if you want to rent wave runners go to Eagle Beach as Geordie recommends, but if you are looking for a great beach experience away from the tourists, go to Havanna Beach Club. It is within walking distance of the port. You can find more details and pictures of it, as well as the other beaches in Aruba at our PortReviews site. Here is the link: