The 'pay as you go' route is fine if you have the time, like, while you're working on your degree; otherwise, in an industry where seniority is everything, the sooner you can get your name on that seniority list, the better. The pay-as-you-go route can easily add a year or more to the process.
I haven't taken the plunge yet, but while I doubt anyone will deny the financial burden of loans on the insulting wages paid, most will also agree that ATP is the quicker route to the proper side of the pay-to-fly/paid-to-fly equation.