@Stone do you *know* that the place you found has powder? Like you’ve been there and seen it? I ask because a few months ago I thought I had found somewhere with Retumbo a friend had been looking for. My LGS had just got a shipment of Hodgdon so I wasn’t all that surprised to see another Hodgdon product finally available, and I sent him the web link. But it turned out to be a scam after he’d “purchased” it. Very embarrassing position for me!
But if it’s a real business and he really has genuine black powder then buy some now whilst it’s available. Swiss is notionally better, but like premium gasoline you probably only really get the benefit of it when you are already shooting at a high level and with premium equipment. YMMV but I would pick whichever one he has most of and is likely to be able to get again…..