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

[Zhalentine]

"It is a blatantly obvious case of special pleading, ie 'everything that has a beginning has a cause, except God'"

No, it's a case of mental flatulence to consider that there is no end to the chain of causality. You're right that the best two arguments are causality and design, but I agree with Frodo, that I would like to see you try to topple them.
Either cause and effect go back in literal infinite quantities (which I forward CAN NOT exist in this reality, we can make a name for the infinite, and pretend to understand it, but it is not real in the sense that it can never happen). So it is special pleading that nothing made the universe, because it seems less likely that there is the impossibility of infinity, and slightly more likely that there is something we haven't figured out yet. you think god is impossible, but I think infinity in reality is more impossible.

And perceived design, also strong. There are a lot of factors that make life, and sentient life possible here today. It is either that they happened by chance, or by design. Either us being here now is fantastic good luck (and the further back, and smaller scale you look, it really is fantastic good) or it is not.

So we have two ideas. One is that the universe never really started, or that the thing that started the universe never really started, or that it did by chance. Then the universe built up to support billions of years of action, and million of life. Tens of thousands of years of advanced hominid life, and a few thousand years of sentience. As much as we can appreciate the beauty of the system, it is all just random. There is no reason that it ended up as such a beautiful machine.

Or, and I think more likely, there is more to the picture, if only because that world view is showing obvious flaws.

Time is simply the period between two points. If I choose any point in time and specify no end, would you agree that time would therefore be infinite? I don't see how you can claim that infinity can not exist...

From what I understand of your post, you believe in a creator because there is a small chance that random events occurred that lead to life? What do you think the odds of are of a creator coming from no where, or simply always existing (a lot more unlikely than random events)? Why do you think the creator coming from no where or always existing is more likely than matter always existing? Perhaps you can connect the dots for me on how you went from something having a low chance of occurring to a creator must exist in order for it to happen.

"Then the universe built up to support billions of years of action, and million of life. Tens of thousands of years of advanced hominid life, and a few thousand years of sentience. As much as we can appreciate the beauty of the system, it is all just random. There is no reason that it ended up as such a beautiful machine."

That sounds a lot like you're saying that the universe built itself up around life, whereas the saying "structure affects function" could never be more true. The universe is the structure and life is the function. Life is building itself around the universe. This can be seen by observing all the species on Earth and what features they have compared to what environment they are in. There is a reason you don't see reptiles in Antarctica, because the structure(cold weather) doesn't support the function (cold blooded animals with no way to generate heat internally)