Stick with his recommendations. The more standard 1 1/2” looks cheap.

Is one more modern or traditional than the other?

No. You seem to prefer thinner so do that

Thanks!

"I know the balusters can’t be more than 4” a part."

That, and the baluster/stair tread ratios could be the driving force behind the baluster width.

Thanks Mark. We can do either 1.75” or 1.5” baluster and still do 2 per tread which I prefer. When I saw the 1.75” baluster, it initially felt bulky to me but maybe takes getting used to. Was more or less wondering what designers/gc/architects would typically do given our dimensions (10.25” wide tread, 6.25” wide newel) and going for a more updated/transitional look.