When you are prepping a rental property, a fresh coat of paint on the inside is an inexpensive way to give you one up on the competition and justify a higher rent.
Pick one color and one brand for all rooms and all rentals. It’ll make your life so much easier. That way you buy the same thing every time. No need storing a bunch of different colors and not having the right one when you need it. I use a very light beige latex (water-based). It goes with everything, hides flaws well, and looks warmer than flat white.
Don’t skimp on quality; you want something that has a decent chance of holding up to kids. I like Behr, but I’m sure there are others that are equally as good. Consumer Reports publishes test results of most manufacturers’ paints and stains.