I prefer DuraCoat. It can be air dried easily on metal, wood and plastic, the colors can be mixed for custom colors and it's very durable. I apply gallons of it a year. Not an endorsement, but my website below has a photo gallery if you want some ideas to go further than single colors. One other thing i really like is that DuraCoat is flexible, while CeraKote is very hard. this allows for a lot of heat resistance, and if you need to do any touch ups you don't need to remove the entire finish as you do with finishes like GunKote. For a cheap alternative Brownell's AlumHyde II works great from a spray can, is pretty durable and easy to apply. prep is the most important thing with any of the spray on finishes.