Grease

I keep a can of just normal black grease in my truck all the time. Take a dab and put it on my hitch ball. When I unhitch, I use a paper towel and wipe off the hitch ball so it won't get all over everything it might tough. I don't think it rally matters what you use, as long as you use it and keep the hitch ball greased. Use what's most convenient for you.