I can't speak much on awareness other than to say it is easier to move as a team, know the critical map points, and the flow of the game mode. On the other hand, I use all of those guns regularly. They're fun. Here's some distinctions between them and notes on usage.
Splash-o-matic:
You're a splattershot with slightly lower range and better fire rate/accuracy. You have to play with the range weakness in mind, trying to avoid head-on confrontations. I prefer the neo variant as the inkzooka and burst bombs both compensate for the shorter range. It takes some finesse to use, I would elect to not use this weapon if you are fighting a lot of S/S+ players. They'll smell your green like a synesthetic from a mile away and carve you up for dinner.
Sploosh-o-matic:
The sploosh is very fun, but its range is a massive weakness. Fortunately, the point sensor gives you the ability to push into enemy ink with a nice safety net. Use it often and learn to love it if you don't already. Beyond that, swim speeds or ninja squid are good choices for the weapon, as you need to utilize squid form to close the gap before assassinating with your high attack power and speed. Kraken synergizes well with this kit, as the point sensors can prevent people from hiding in their ink. Although this is maybe one of the easiest weapons to get kills with, I don't think it's as effective at playing the objective as the others you've listed. This is mainly due to its lack of range and offensive sub weapons with any variant.
.52 gal:
Its slow fire rate and spread means you can't let people get close. Initiate your attacks around chokes and places with good cover, while using the splash wall to deny the enemy the ability to reach you. One damage up main is nice to take here, as a single defense up turns the .52 gal into a three shot kill, which hugely harms its viability. This weapon is a favorite of mine in splat zones, as it kills quickly, denies access to the splat zone, and the killer wail is an effective zoning tool to push the enemy team out of the ink if they're on defense. Beyond that, this weapon is probably the easiest of the four to do well with.
Mini splatling:
Use the zink variant and play it as support, it has the lowest learning curve. Harass the enemy by lobbing your disruptors and stay alive to ensure you can crank out bubblers for your team to make a push. Engaging behind a teammate, you can seriously put out some respectable pressure, as your charge rate is berserk. The main downside to playing this weapon is its pitiful range means to secure kills by yourself, you usually have to put yourself in harms way, something that is exclusive to the mini splatling.