On the job training definitely beats all. I started at PVTI, then went co-op (which means half day school-half day on the job). I found that I did learn more on the job. After all, it's the "real" world.
It's just a matter of finding the right company that will hire you to give you that chance. Most likely, you'll have to start at the bottom and work your way up. At least this way, you can learn all the "in's and out's" of the automotive body shop industry.
Some companies will even help you get certified, whether it's ASE, I-CAR, PPG, Glasurit (usually the paint line they use)...In fact, I haven't paid for any of my certification schooling, the companies I worked for took care of the tab.
I personally like working for "dealership body shops". Most of them work with top level insurance companies. The insurance companies want to see body shops have their employees certified, therefore, they must pay for the training
just to keep the insurance company happy.
the body shops also like display they are a "Glasurit" (example) certified shop, which means that all painters must be certified, again, the body shop will pay the tab for this