At the beach, what is the best couch material if the place will be used as a rental?
We need to buy a couch and chair for our condo at the beach that will be used as a rental. We want to buy something that is of decent quality so that it lasts more than a season or two. We want furniture that will not get destroyed easily from wet bathing suits and spilling of drinks.

Your best bet would be outdoor furniture with a metal or wood frame and separate cushions with weatherfproof fabric or machine washable zip-off covers. There are hundreds of varieties to choose from nowadays. I've got 2 outdoor porches and a patio and I've gotten outdoor furniture for them that is so comfortable and attractive that I use it indoors during the winter as well. Besides food and wet bathing suits you have to deal with sand -- frame and cushion furniture won't collect sand down in the upholstery like regular sofas will.