I have used Pledge with good results, but Rain-X now makes a product specifically for plastics...and it works fantastic for repelling water.
Since most golf carts don't have wipers, it's wonderful to be able to see perfectly because the water forms large beads that roll right down the windshield when caught in a downpour.
Rain-X(R) Plastic Water Repellent - Rain-X
I'm afraid to mix the Pledge and Rain-X, so have been washing the windshield first with a microfiber cloth and water with a small amount of soap...before putting on the Rain-X.
I've been a huge Rain-X advocate since spending a lot of time in helicopters back in the early 80's and that was the only thing the pilots would use.