With plated bullets in a .38, I prefer using Hodgdon HP38, which by the way, is the same exact powder as W231. As the name implies, it is Hodgdon Powder for .38 Special (and is $2 per pound cheaper without the Winchester Horsey on the label).
Load data for both Hodgdon and Winchester here -> http://data.hodgdon.com/main_menu.asp

With jacketed bullets in .38 spl, HP38/W231, Titegroup, or Unique.

For .357 Magnum, Alliant 2400 is my go-to powder although I have a pound of Power Pistol I've been hankering to try...