I'd say for PS4 DB Games, FighterZ >> Xenoverse 2. FighterZ's combat feels very balanced in terms of both character usage and skill difference between players, plus it's battles are fast paced with few lasting much longer than a minute. Compared to that Xenoverse 2's Parallel Quests tend to stretch on for around 10 minutes for the later ones and become a repetitive grind, not to mention the terrible RNG system.
That's not to say FighterZ is perfect, as it still has a lot of flaws that stop it from being the best DB game as many say it is. For one, Super attacks can be frustrating to pull off due to needing to move the analogue stick in a very precise manner. There's also the flaws in combat of it being extremely difficult to do anything to an opponent once they get you in the corner and start hammering you relentlessly, not to mention Sparking Blast being so much of a game changer that it's completely broken if used right. Also, the main lobby and server reliability is absolute trash, as well as some online features such as Arena Match being pretty pointless. Once you've completed all the story arcs, done arcade and played a significant amount of online battles, there's also not much left to do in the game either.
Still one of the best DB Games, but still ranks below Budokai 3, Tenkaichi 3 and Raging Blast 2 for those issues.