Both powders have their place. Triple Seven is a good powder. It is powerful, seems to ignite well if you have a good flame source, cleans easy and is reasonable in cost if you catch it on sale. BUT some, not all rifles, develop a crud ring near the breech when you shoot it. So you have to pay some special attention to that area. Normally it will clean up with simple water.

Goex or Black Powder cleans with water, I have shot up to ten shots in traditional rifles without swabbing the barrel. It ignites the easiest of all the powders. And it is consistent. If I have a rifle that is giving me fits on the range, I go to Goex. There are many brands of black powder. Like Lee said, some better then the other. The only black powder I refuse to purchase is called Elephant. The favorites because of price and performance is Goex or Graf's and Sons black powder, made by Wano.