I choose to believe in God.
I respectfully submit for your consideration that the Bible is what you actually
choose to believe in. Without the Bible, God is undefined.
You may believe there is "a god" without the Bible. But not "God."
The universe is full of mysteries and wonders. It's easy to see why people
can believe there is something more, beyond what we see and touch. The
concept of "a god" is not at all surprising to believe in.
Believing in "God" is another matter. It requires as a prerequisite belief in
the Bible. Some of it or all of it. Without the Bible there is no defined "God"
to believe in.
When asked questions of their faith in God, the "Bible Believing Christian"
responds with scripture. The basis and source of their faith. This alone
demonstrates (or strongly suggests) their belief is in the Bible, and only
by extension, in the God of the Bible.
You choose to believe in God (the God of the Bible) because you choose
to first believe (in) the Bible.