For bullets, 180-200 grains if you want to make a super-light plinking load for yourself or to let others shoot. 240s can be loaded down, but still create a bit of a push. If you don't mind, 240s all the way. Shell out a couple extra bucks and get coated to avoid blackpowder-level clouds of lube-smoke.

For powders, I recommend one of the ones that burn. No, really, it's that simple. I make plinkers out of whatever fast-ish powder I feel like getting rid of. I like 2400 for full-power over H110/WW296 and such, and I've got a pound of Power Pistol I'm aching to play around with. Unique falls in the middle, and is useful if you don't want to goof around with multiple powders, but I don't find it as good as more specialized options.