If I am correct, Microsoft considered the XBOX 360 a complete project, which is why Roblox is unable to allow playing from the XBOX 360. A quick internet search for XBOX 360 vs XBOX One specs brought me this: In case specs matter, the XBOX One has better specs overall, but I am not sure what to think of the "Fee for used games".
Xbox1 is good but Xbox 360 is what I was used to, to me it's more helpful to connect with friends then the 1.
Xbox One has better specs (gets higher fps graphics), and won't get outdated soon. Xbox 360 has lower price and gets lower fps. They doesn't support some next gen games, too, and soon, it will get outdated.