I use the thunderbird finishes.
The polyurethane sprays on a laquer then converts itself to a urethane after about six hours. Drys real fast and is great if spraying conditions aren't the best. Drawback- if you need to touch up a spot after it's cured, you can't just respray it with the poly.
The epoxy is a two part system that is the most durable and sprays on very nice. Drawback- drying time. It stays tacky for an hour plus. You should wait about three hours between coats and a few days before buffing.
In a nutshell I like different things about each. I wish the epoxy dried as fast as the poly.
I've never used any other finish and have always been pleased with the results. Mike