One powder for target 38 spl and hunting 357?? That is asking a lot. You won't get the best results out of the 357 with a powder that will do well in 38 target loads.

But if I had to pick a powder, I'd say Unique. 4.5 grns for the 38 and 7.5 grns for the 357, both with a 158 grain cast pill.

Now, that being said, I would still rather see you use Unique for target loads and a powder along the lines of Alliant 2400, H110/W296, or AA#9 for the hunting rounds. With hunting rounds, the faster and heavier the better. I don't hunt with my 357, but if I did, I would go for a 180 grain XTP or a flat metplat cast bullet in the same weight.