Samurai I would say it depends on what is your goal / what type of player are you.
If you are "weekend player" who likes to run and gun => Phantom probably is the choice. As said above easier to control, more accurate in its "inaccurate" phase. Also from my experience faster rate of fire does yield more kills in situations where you and your enemy spray eachother.
Another point as mentioned partially above = silencer. In lower ELO lobbies people are really bad with sound queues and more often than not (not like 9 out of 10 time but more like 2-3 out of 10 times) will not arrive in time to help their teammates being shot by you / will get confused where you are.
Also might be a bit more helpful to yourself as while shooting Vandal I personally hardly hear what is going on around me, things is damn loud, while doing the same with Phantom I actually can switch targets more successfully.
Finally if you want to get good in 1v1s and 1 tapping people, probably the best gun is Guardian, it just forces you to aim at the head + is much more consistent even in comparison to Vandal where you sometimes actually miss the head being really close to it / Guardian for me yields results much more consistently, same as Sheriff.
Pros use Vandal more because they often get into 1v2 situations and at that level you are just too slow with Guardian / can't be that consistent hitting 2 headshots in a row -> Vandal is used to 1tap first enemy and then spray transfer (keep holding mouse1 while transferring and tracking 2nd target) to the other to potentially get 2 kills.
p.s. please don't be that person who comes to Competitive mode and does not play Vandal with a comment "I can't control it" 🙂