Here are my thoughts on all of these, which I am writing in advance and saving to post until after a while to see what all conversation and thoughts people have about it.
For Yellow, but 50 ms is quite a lot. It's pretty hard for me to gauge exactly how many situations you find yourself in where it's what makes a difference but this is going to be at least some degree of impactful regardless of how good of a player you are, plus the fact that it's instant would be a pretty big bonus for a lot of people. If you want a boost that feels more subtle, but still lets you see some form of boost in your results, then I guess there's nothing that really compares to this one.
For Green, I think you take this if you want to exist only as a solo queue demon and don't care about competitive play although it might still have an argument for competitive play. There are a handful of weapons that are strong in solo queue that don't quite translate as well to competitive play, like the Tri-Stringer or Luna Blaster. The former is especially noteworthy because as a weapon, the only thing holding the Tri-Stringer down is that it's simply outclassed by other options as opposed to explicitly being bad. Would a godlike Tri-Stringer player be better than a good Snipewriter if a comp was built to support it? It's hard to say, probably not but maybe for some weapons.
For Orange, it'd be nice to feel like you're always playing at your best but not as strongly beneficial as some others here are. Maybe this makes the game more fun for you and I'd understand picking it on that merit alone. The rest of these are all either better for the sake of improving at the game or at least can provide some other tangible benefit or interesting scenario that this one doesn't.
For Red, funny enough, this one was 3x in the original Melee version and everyone was saying this was the one you go for. Toning it down to 1.5x I still think this has a good case for the best choice if your goal is to get better at the game. There's a pretty strong correlation I see where the more time someone spends on the game, the better they usually are, and 1.5x is a big boost. Comparing myself with around 2000 hours on the game to someone I know with 3000 and the difference is night and day. I think this is your go-to for improvement regardless and is the one I would personally pick for that reason.
For Pink, I think it's strong for similar reasons as Red, but overall is not as good. Pink has no bearings on how good your mechanics are and will start to become less useful when you get to top level and have top-level coaches all around you as is. Very good for someone just starting out though and there will be some more specific, mid-match things that this would always help you pinpoint that a fellow top player couldn't get to until after the game.
For Gray, I remember the opinion someone said with Melee where this pill's equivalent there will turn you into ultimate content creation machine. If that interests you then I could see someone picking this for that alone. Otherwise I think this is still one of the strongest options available. Splatoon is a very hard game to play from disadvantage and being able to force that onto your opponents every single time at the very start is a huge deal, especially on maps like Barnacle where lockout is difficult to recover from. Imagine being able to coordinate this with your teammates too where you know you can go in and get a quad while your teammates paint for special or something.
For Black, this is probably one of the weaker ones overall but would make practicing specific things a bit more straightforward. For a while I've struggled to get adequate experience practicing against Triple Splashdown or alongside Tacticooler and this would help that. Might also be fine for grinding out solo queue if you wanted to continuously give your team a Snipewriter and your opponents an Undercover Brella for example. I don't know how good doing that would be at top-level play since ultimately top players are playing a completely different game than I am but maybe it wouldn't even be bad there either.
For Blue, I think what makes it interesting is the team comps that you would be able to open up. A handful of weapons like Rapid Blaster Pro and Tri-Slosher Nouveau go from fringe to viable in your hands, not to mention things like Snipewriter effectively being reverted from their nerfs. Everyone would kind of have to know that you're effected by this and a lot of people would want you on their team because of that. Does this sound fun to you? If it does then there's no other option that's similar. If not then there isn't much reason to pick this over something else.
For Purple, well you get a brewing addiction and might get sent to prison or die at a young age. It's a sad thought that there are probably some Splatoon players who would completely unironically pick this over any other option but it's a funny thought if the person we're talking about is not a junkie.
So overall,
Top Tier - Red, Gray
High Tier - Yellow
Big Gap
Mid Tier - Pink, Black, Green
Low Tier - Blue, Orange
Lol - Purple
Red and Gray are the two that I think give both strong benefit when you're starting out and will continue pushing you ahead as you get to top level, with there being easy room to become so strong that even other top players likely struggling to reach you. Yellow I think has a decent argument but I'm not convinced it can push you to quite the same heights. The rest may have some merit if you think it'd make your time on the game more fun, in particular I might be underrating Black since something like Clash Neo will severely limit opposing comps at a top level, but otherwise likely aren't relevant if your goal is to get better.
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