Invest or pay off debt, which one is better?

It depends on the price of debt. If the price is negative or if you feel you are protected from default on it (which is the same), get as much debt as you can. And invest, spend or just waste money. Never, never, ever pay off more debt then necessary minimum.

TL;DR: Pay off the debt.

It seems like there is always a tug of war between these questions every decade or so, and I'm not really sure why. I guess in the US we make access to credit so dad blame easy that people can practically fall off a log into a credit card? Or perhaps its due to lack of useful financial education in elementary/middle/high school/college(!?) to inform new generations that saving money is a Good Thing.