For the 38 special the only powder I use is Vihtavouri 3N37. It meters very well, is clean shooting, not at all position sensitive, and it's a nice low flash powder for the 38 special. BTW the ONLY bullet I load 38 special with is a 125 grain plated from either Extreme or Rainier. Because 38 special for me is specifically for training new shooters or working on my double action trigger technique.
For 357 Magnum I'm sort of all over the map. Because I have revolvers with 4 and 6 inch barrels plus two rifles in 357 Magnum. As a result I load with 125, 140, and 158 grain Hornady XTP's in both Handgun and Rifle configurations and 158 grain Berry's Hard Cast for Cowboy Silhouette Matches. Yeah, I shoot the 357, I like the challenge and I am not so interested in winning that I game the system. Plus I've found that the 357 feeds a lot smoother in my Winchester. So, I have a bunch of different powders I can use for 357 Magnum.
For Handgun loads my preferred powders are Accurate #5, #7, and #9. Because they meter superbly and I can select a burn rate for a specific bullet. Generally #5 goes to the 125 grain XTP's, #7 to the hard cast and 140 grain XTP's, and #9 to the 158 grain XTP's. If I run out of one of the Accurate powders my fallback powders are the 3N37, Unique, and Longshot. You may also not that I do NOT load my handgun loads with H110 and there is a reason for that. I find that H110 in a handgun produces way too much muzzle flash and that BAHOOM muzzle blast can get tiresome rather quickly.
For my Rifle loads I'll choose a slower powder for the Jacketed bullets and usually load with Accurate #5 with the Hardcast bullets. Because I've found that #5 limits the velocity produced from my rifles and I don't have to deal with leading in the barrel. As for specific powders, my preferred powder for Rifle loads is H110/296. I just love the way this powder performs in a rifle and it meters wonderfully. However, as a consequence of the recent powder shortages I've learned to accumulate some fallback stock so I have a couple pounds of 4227 and 2400 in my stash for just in case.