If we're speaking purely personal opinions, I generally separate my 3 mains in these 3 ways, for these reasons:
Splat Zones: Any Dynamo Roller, because of its excellent turf coverage and ability to reclaim zones extremely quickly and safely, via its main attack flings, Sprinklers or Inkstrikes. Generally, ability to ink turf and defend are key in this mode. Dynamo can do both exceedingly well.
Tower Control: Tri-Slosher, or really any Slosher, depending on the stage, because of its ability to hold down the tower (thanks to range + defensive pressure options), provide pressure over walls while the tower is turning a corner, and ability to take out enemy squids on a tower from high platforms. The Tri variant loses the range, but can easily and quickly clear a tower and take out enemy squids from below / ground approaches. Squelchers are pretty solid contenders for similar reasons, and they've got even more range .
Rainmaker: Octobrush Nouveau, because CQC flanks and aggression, from an offensive and defensive standpoint, can be extremely important in this mode. Enemy Rainmaker holders need to be taken out quickly in many scenarios (because just a few more steps of advancement can cause a loss), so quick-to-kill/1HKO weapons are generally really useful here. Trying to purely outrange Rainmaker tornadoes can sometimes end badly lol, especially because the really long range weapons are all slow and have poor mobility. In many cases, I've found it's better to utilize stealth and speed here. You just have to assess your risks wisely.
Granted, as you've noticed I don't use shooters lol so can't make many alternative recommendations there. If you wanna go the OU route, Tentateks are probably the most versatile weapons in the game and can handle most situations without a huge amount of trouble. Their main setback is they fall solidly in the mid-range category, so they aren't always the best candidate to hold down a tower if you've got a lot of long-range opponents. And then, y'know...you could always join the standard parade of Gals and Lunas, if that's your thing.