Speaking from years of painting experience. Metalic black tends to look dirty even when its freshly washed clean. Black also shows any, and all imperfections in the sheet metal. As far as manufactures of paint. I am a DuPont fan, one reason is they make a good product. I also learned with DuPont, so I am partial to it. There are many brands of paint. Just keep in mind you tend to get what you pay for. Nason is DuPont's off brand I have used Nason on many rigs, its a good product. As Omni is PPG's off brand. Personally I like Omni single stage better than PPG. I have used Western, 5 star, Sherwin Williams, Martin Senior, Kirker, etc. etc. Wasn't real impressed with Kirker or Martin Senior. But that was years ago. they might have improved since then. I have Western on Yellow Snow, its held up quit well. It hasn;'t been waxed ever since I painted it, its the rust, and snow bank damage that is the demise of that paint job.
Also keep in mind the finished paint job will reflect all the body work, good, and even more so bad.
Key to any paint job is quality body repairs, good prep, blow out every nook and cranny of the vehicle several to a dozen times with air. Use top quality masking with tape, and paper. 3M, and Norton both make good masking tape. No $1.99 Wal Mart tape, none of that blue painters tape garbage. No news paper! When you think the area your going to spray in is clean, reclean it, blow all the walls, and anything that is to stay in the room while painting off with good charge of air. Sweep the floor out the door with water. Keep the floor wet while painting too.