Terminal

It depends on your need, usually, the X8 is much cheaper. So if you don't have a 4K TV. I would recommend you the X8. It allows you to record 8 tv show at the times, as much as the 4K. You have pretty much the same storage. The 4K is just a little bit faster. 

Here a nice page that allows you to compare : 

http://www.videotron.com/residential/television/terminals-and-accessories

Kind regard, 

Yass