Paint them before installing them, and be sure and take the doors off including the hinges and any end panels. That way you won't end up with places where there isn't paint.

You're going to want to clean and sand them good, and possibly prime them so seach youtube for DIY videos on how to do it properly. And be sure and buy paint designed for cabinets.

It's more work, but you will get a better result painting after installation. Prep them first, including a coat of primer before. Install, get everything to fit -- you may need to sand, putty etc. Spot prime, sand and paint. Paint the doors and other removable items off the cabinets.

I saw on HGTV they painted the cabinets after the install. Happy I saw your reply.