Lots of good powders out there for the 223/5.56, some are ball type and some are "rat ****". If you are going to load volume and use you RCBS Powder measure I would start out with a good ball type powder. That would be Tac, 2230, X-T, 335, 748, or 2460.
If you are loading for blasting ammo it's hard to beat the Hornady 55gr FMJ. They shoot pretty good and are cheap. If accuracy is your goal then I would start out with Sierra, Hornady V-Max or Nosler BT. My vavorite bullet for my Colt is 53gr Sierra HP.