One of the primary mistakes I see among both the atheist/agnostic group and the majority of theist groups is that they beg the question and commit other forms of logical fallacies.
I am a theist and I believe a God for philosophical reasons. I have not personally come to terms with belief in the Christian God,
but time will tell to see if I am convinced of the christian arguments.
The ontological argument I find to be preferable is St. Thomas Aquinas' The existence of an Unmoved Mover.

Here is the best presentation I have seen of this argument:
>https://youtu.be/BAIHs5TJRqQ