Any of the real black powders or Pyrodex would be a good starter powder. There's a learning curve with muzzleloaders and any of these powders fit right in with what you will be learning. To get the hang of things you might find it easier to buy the bullet/sabot combos sold in stores in the clam packs. It won't take you long to move right into more advanced ideas/areas so don't spend a ton of money to get started. Triple & powders and Pyrodex off pellets and you may want to use those at first, but with any powder you'll want and need to develope very good cleaning practices the same day you shoot to prevent any rust or corrosion that comes with shooting black powder guns.
Keep reading here, Ask questions. Stay alert when you begin to avoid distractions, but relax and enjoy the shooting time.