Hot to choose the paint

Pretty much comes down to budget. Of course not everyone is made of money and all cars don't warrant thousands in materials and the top of the line products. But with the affordability of many of the urethanes and 2k products today (Okay, not cheap, but if you factor in added life and the material being higher solids, less upkeep required compared to others), it doesn't make too much sense to use 1k products, lacquers or enamels.

Of course not all urethanes and basecoats are created equal, but even a cheap one should be better then an enamel, and the price may not be all that much different.

Hard to not recommend using an epoxy considering the corrosion protection, sealing propertys, wide compatabilty it has and the limited potential for problems it has for the price. Just be sure your surface temperatures are above 60 when applying it. If there is a problem with epoxy, it normally from shortcuts or products like rust bullet or acid containing products causing the problem.

Basecoat clearcoat urethanes and polyurethanes are most widely used today, because of the good durability and life they have with little upkeep needed. Also with so many colors being metallics and pearls in use today, A basecoat is easier to apply them in, and clearcoat provides better uv protection to the color, which is why you don't see colors fading and oxidizing like so many years ago. A basecoat clearcoat makes for easier repair in the event of an error during application and after application, and imperfections can be sanded and buffed afterwards. A metallic or pearl color in a single stage (without a clear) cannot, and pretty much have to live with how applied unless repainted. Many still use singlestage, but majority limit use to shooting solid colors.

I would maybe consider using an acrylic enamel with a hardener on a real budget job or for originality, but often a cheaper urethane can be found and not be much of a cost difference.

Lacquer is a goner. Sure it can look nice(Lacquer paint has to be buffed to get good gloss), but the durability just isn't there (even more so with the lead removed today) and needs good care and kept garaged. Not even cheap either when you consider your paying for a lot of solvent(and the country is really pushing for green eco friendly product use) , and with the low solids requires a lot more coats to get proper film build. There is a good reason it was phazed out years ago, and most don't miss it. Maybe, but not likely, if someone was really hung up on originality and the fact the car originally had lacquer.
With the acception of Maaco and other production paint places, Yep, most shops are going to most often shoot a car using a basecoat/ clearcoat urethane, with 2k undercoats underneath.