Tim,
I chose PPG only because I have a large PPG dealer in town. I did not want to buy my paint thru the mail, for the simple reason that if I run out of something, I did not want to have to wait for more solvents/paint.
IMHO, there is not enough difference between brands of Automotive Acrylic Urethanes to worry over. Local painting advice and a fully stocked dealership are more important to us amateur painters.
On the subject of pricing, I realized that the size of my order for an airplane was much larger than most body shops in town, particularly when purchased all at once. So, I made a list of everything I though I'd need and called around to towns within a 100 mile radius and let them all know that the order was going to the lowest bidder. As it turned out, the PPG dealer 60 minutes away got the order because he was $500 lower than the guy in town, and he delivered it to me.
Like the trucking business, paint is highly competitive and negotiated, so use your own volume advantage. Also, whatever brand you use, cross check any advice your dealer gives you with the manufacturer's technical support line. Your dealer can get you the number. I did the whole plane with 1Gal sandable primer (blocking primer), 1Gal Epoxy primer, 2Qts metal cleaner, 2QTs alodine, 2.5 gals of color (single color). Let's not forget sandpaper, reducers, retarder, activator. Oh and cleanup stuff: Acetone and lacquer thinner (home depot 5 gal cans).
Good luck,
Art in Asheville