Since I'm into competitive debate proving god exists for 15 minutes might be a requirement in the future... Well, I think the most convincing argument to any audience is something connected to the cosmology and design of the universe - Saying there had to be a first cause, and that there's things science can't explain like the human mind and conscience. I would also throw a sophisticated version of Pascal's wager 
Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you
