My recommendation would be Pre-Calc Junior year (Honors if available which gets the extra honors weighting at most HS’s) and Calculus either Regular/Honors or AP Senior year or AP Stats Senior year. Majority of the UC’s require at least 1 quarter/1 semester of Calculus or a Math general ed course regardless of major.
How is he doing in his current Math course?
How many AP’s does he have scheduled for Junior year?
AP Stats is considered a “light” AP so this one class will not make a huge impact for rigor but Pre-Calc would be the natural math progression as a HS student. If he plans to take Physics Senior year, Pre-Calc would be far more helpful than Stats.
For the UC’s, even though he is not considering a STEM major, a year of Biology/Chemistry and/or Physics is still recommended to be competitive.