Choosing the best Final Fantasy 15 version largely depends on what you can and cannot put up with, when it comes to visuals and performance.
In the video, Digital Foundry checks the frame-rate on the Xbox One version to see if it manages to offer a locked 30fps frame-rate, and whether it suffers from frame-pacing issues seen on Sony's consoles.
Right off the bat, the game does have a lower image quality overall on Xbox One, as the resolution goes only up to 900p, compared to 1080p on PS4. This means it can go even lower, thanks to its adaptive resolution technique.
However, frame-pacing is as it should be on Xbox One, a definite improvement over PS4 and PS4 Pro in this aspect, which results in a smoother-looking game. That said, drops below 30fps do happen, but they're very short and generally don't go below 27fps.
In short: you'll either have to put up with reduced image quality on Xbox One, or frame-pacing problems on PS4 and PS4 Pro.