We got the best bang-for-buck, best color library, and best coverage (less color needed to achieve final result) with Standox. I've also used DuPont & Nason, which were also from the same parent company, PPG, Sikkens and a couple of the "budget" brands. Spies-Hecker had their fans as well.
You do get what you pay for in most respects. My Standox cars are going on 30 years and the paint looks as good as ever. My truck with Nason on it is going on 9 years, still looks the same.
All were 2-part BC/CC jobs, using the recommended system (primer, sealer, etc). Also did a Nason base with a DuPont clear that came out nice & has held up fine.