This topic can definitely stir up some debate.
If possible, I would say get both. They are too different to compare in many ways.
But, they are still comparable at the same time, as contradicting as that is. I would argue for Genesis simply because it is more recent, and the production quality is much higher, and the explanations come in many forms. Plus, many of the XCM moves taught on Xtreme Beginnerz are outdated. Not all of them, like the fundamentals and such are still taught well, but the more unique ones are very old-school.
I learned from XB to begin with, but I think Genesis might have been more effective if I started out with that. I'm only 2 years into flourishing though.
Anyways, both if you can, but if you can only afford one, Genesis would be my honest suggestion.