So is LW for people who think highly rationally, or for atheists who think highly rationally?

Neither, really. It's for people who are interested in epistemic and instrumental rationality.
There are a number of such folks here who identify as theists, though the majority don't.

Without any empirical evidence either way, is it more likely that there is some sort of Deity or that there isn't?

Can you clarify what you mean by "some sort of Deity"? It's difficult to have a coherent conversation about evidence for X without a shared understanding of what X is.