What is the best portable hard drive for Xbox One X?
Honestly, if you have the increased budget, I would take full advantage of that USB 3.0 port on your Xbox One and go with a portable SSD. Seagate makes purpose-built solutions with their Game Drive series and if you want more options you could grab the Samsung T5 or SanDisk Extreme; both are solid drives.
If the budget isn't there or if you just want more capacity for games, Seagate has two options; Game Drive 4TB or Game Drive Hub 8TB. Once again you can break away from the "gaming" drive and save money by purchasing a Backup Plus 4TB from Seagate or My Passport 4TB from WD.
Hope this helps you out!