best degreaser to use before paint

If you are talking about the entire cleaning process, then a thorough cleaning with something like Simple Green followed by a thorough cleaning with dish washing soap, followed by time to completely dry followed by a final cleaning with an automotive grade wax and degreaser will prep for any paint. If you just are talking about the final cleaning before paint, then use an automotive grade wax and degreaser. I have used a LOT of wax and degreasers over the years, and I think I like Eastwood's 'Pre' cleaner best. It comes in easy-to-use spray cans. It's just called Pre.