in splatoon, since map control is so crucial it's important to have a set that helps you with that. anything that's noncommital is going to be good, since the time to kill is so fast, and breaking into enemy territory is a crucial skill to have because they have access to squid form in it, so it's important to able to run away from a fight gone awry and come back when you think it's appropriate. so when i say noncommital sets will be good, that's to say that anything that lets you set up an engagement and/or take control of one is good.
because of this, i wouldn't want too many rollers on my team. they're ok with ink coverage, sure, but because they can't really cover ink in front of them besides meagerly flicking the roller, that makes them a passive, defensive class, and if they want to get frags they have to smartly flank to get the instakill. they remind me a lot of the pre-2013 axtinguisher/degreaser set up in tf2; they're a threat to be aware of, but if you're careful with your position and are aware of what's going on around you, you'll be fine. this is especially true because of the map; even if you can't see the enemy team directly on it, you can see all the ink being covered up, so you can see a roller coming into your territory by the long trail of ink going through it on the map.
chargers... we'll see. i wouldn't want too many of them either, since if they can't directly help you from their effective distance, if they're not doing so well it turns firefights into 3v4s (assuming there's only one charger on your team.) there's a lot of benefits to having a charger, such as mid/long range support that can pick off key targets, firing ink in a straight line to swim up for rollouts, etc, but they're not a versatile class in a game where being adaptable is paramount.
shooters are very important to have since they're very general, adaptable weapons. they're probably the best in terms of ink coverage since they can shoot in front of them rapidly, allowing them to be aggressive with it (and it's more important to cover enemy ink than dry land, since inking over it gives you more percentage and they lose than percentage) and gives them a variety of movement options. even ignoring the hypothetical techniques like splatdashes/splatterhops they have immediate access to mobility options that gives them an advantage - you can ink up walls to get high ground, for example, much faster than a charger or roller can (unless you're using the ink brush.) since they're good tools for movement, ink coverage, and fragging, i'd want most of my team to be composed of them.
what weapons would i want my team to use, hypothetically?
- the forge splattershot pro with the point sensor and inkzooka will be an amazing set for safely engaging the other team, since you can tag enemies with the point sensor and the splattershot pro has possibly the longest range out of any of the shooters we've seen. a fight isn't a commitment since you can squid out of their range and hit them while they can't hit you, and if they get smart and get out of the fight before they lose it, you can hit them with the point sensor for someone else to find them and finish them off. it's nice that the inkzooka is its special, too, since you can spam it and take enemy territory without losing ink, or go for safe frags.
- the aerospray rg with the ink mine and inkstrike is a very all purpose loadout without much drawbacks to it. the aerospray is similar to the splattershot jr, but with a faster fire rate and less damage, however they're practically the same weapon since the time to kill is about the same because of the rate of fire. the biggest differences the aerospray and jr. will have is which one has the least wide spray, but both seem to be pretty wide; however, that's to their advantage. they're great tools for ink coverage since they cover so much ground in so little time. the only drawback is that they don't have much range to them, but not every map is going to have very open sights to begin with, and it's not hard to position yourself for a frag. the ink mine is a good sub because it's so noncommittal; just plop it down where the other teams players like to run through, squid out so you'll get the ink back, and you might get a free frag. if someone finds it with an ability like bomb sniffer or can just tell that it's there and sets it off, that's fine, you really haven't lost anything. the only downside to it is that if you're not getting any free frags with it, you could hypothetically be using mg set with the seeker for better results, but if you do you'll lose the inkstrike, which is a great special. its basically free area denial since it creates a wide "no enemy team here" zone thats an instakill when theyre hit, coats the radius with your ink, and you don't have to be anywhere near where you want it to land.
- classic squiffler with point sensor and bubbler is probably the best charger if you want to be a team player, imo. it's not long range range, sure, so you have to position yourself closer to your team, but that's an advantage, i think. it also charges at a much faster rate, and is still a one hit kill when fully charged, so you can support your team by getting assassinations, and throw the point sensor at key targets for your team to track. the bubbler is basically an ubercharge, in the sense that it makes a push safe, so this is definitely a team-player weapon.
- ink brush looks interesting since it's a roller you want to flick a lot, but we'll have to see once it comes out
this is all hypothetical, though, and are just the sets that i've thought about the longest. we'll see which sets turn out to be the most favorable once the game's out.