Ranking of all specials for Splat Zones only.
Honestly I'd bump Reefslider up to Vac level because the two are in pretty similar spots for me, especially for Zones.
Vac is able to absorb enemy fire for a bit, especially on more cramped zones, can be used safely from a distance to either cheese the zone or send a nuke at the enemy; however it also takes a while to charge, is not guaranteed to actually work given that Stampers and some rollers are quite prevalent rn (or even people splatting you once you fully charge) and your mobility plummets as soon as you absorb even the tiniest bit of ink.
Reef on the other hand is more consistent in at least going off, is much faster at actually doing something (even if most of the time it will also just be zone cheese) and is a bit more generous than Vac in terms of damage since unlike Vac at least Reefslider does splash damage. However in cases where there aren't any Splatanas or Rollers around, the user is MUCH more vulnerable than Ink Vac (though after actually achieving something) and has much less range.
Basically what I'm getting at is that both specials are equally mediocre as hell and should be fundamentally reworked to actually let them function.