Christians, what is your VERY BEST arguments for the existence of God?

[Darwinian]

All that modern cosmology says is that the universe that we know and love came into existence 13.7 billion years ago in the form of a big bang. Although this is not really the best description. A better description would be a sudden and unstoppable expansion of a singularity which then caused inflation.

We do not know that time started at this point as we cannot peer beyond it. As far as we know this singularity which has lead to our universe had always existed so, in keeping with Occams Razor it's better to say that the singularity and therefore the Universe has no cause, to keep things clean and simple.