As to powders: I do try and keep the pistol powders to 1 or 2. Win231 for most everything and IMR4227 or 2400 for 357 Mag, and maybe Unique or Bullseye or 45 Colt.
Since I haven't found 231 in a while, I've been loading 9mm, 40 S&W, and 38 Spcl (will do 45 ACP) with WST. I also picked up some Promo (Red Dot) and will develop loads for 9mm, 40 S&W, 38 Spcl and 45 ACP.
On rifle powders I have learned what Archangel says is true. You can't get away with only 1 or 2 powders.
I load or will load for a large variety of cartridges. 223 Rem, 308, 30-06, 6.5x55 Swede, 8mm Mauser, 7.5x55 Swiss, 303 Brit, 30-40 Krag, 7.7 Jap and 6.5 Jap.
I like BL-(C)2 and RL-15 but haven't seen them in a while. Just got some LT32 that I will be trying in 223 and 308. I have some XMR4064 and a few others to play with the other calibers.