I suppose your main weapon is the one you're most comfortable with, secondaries would be ones you can use, but don't like as much (whether it's because they don't quite gel with your playstyle like the main does, or they're very different weapons you pull out when you think it's time for a change of pace), and tertiaries would just be other weapons you dust off on occasion.
For me, the only thing I can choose as my main is the Octobrush. It just works really well with my playstyle; I like to attack aggressively, and the Octobrush's decent range, respectable power and great movement speed make it exceptional for me. I can engage enemies and win fairly consistently, Squid Beakons are good to drop when I have a moment to myself so I can jump back in when I get splatted, and the Kraken is good for running away or performing ambushes (though it's not a good attack special, it doesn't have the range for that). It doesn't have any way to attack beyond swing range, but other than that it doesn't have much in the way of flaws. It's a very balanced weapon, though one that lends itself to my kind of playstyle.
For secondaries, there are a few.
First, the Splat Roller. I love how versatile it is, it's like a Tentatek Splattershot in Roller form (and without Inkzooka, but Killer Wail is good). It's not as fast as the Octobrush, which is my main problem with it, and its range isn't as much as the Dynamo Roller's, though Suction Bombs can help with that, but it brings good midrange swings (though a Damage Up feels necessary to get splats near the edge of my range), a wide inkpath when I roll with it, decent long range attack ability through Suction Bombs, and a full-stage-long GTFO in the Killer Wail, which makes it fairly solid for any situation. I'm not as used to using it as I used to be, but it's making a comeback lately.
Second, the Gold Dynamo Roller. A longer-ranged alternative to the Splat Roller, packing HUGESWINGS for great mid-long-ish-range attacks, Splat Bombs for when I don't have a second to wind up (or want to throw it over a wall, or up to a higher area), and Inkstrike to hit anywhere (THERE IS NO ESCAPE. THE INKNADO WILL FIND YOU). However, its attacks are slow, making rolling near useless and close combat undesirable, basically the opposite of other Rollers. Still, it's good, but I'm still learning it (and I'm not as good at throwing Splat Bombsas I could be). I find myself thinking I'm using a Charger when I use this Roller; is that weird?
Speaking of Chargers, my third secondary is the E-Liter 3K Scope. It seems a bit odd to play aggressively with a Charger... and it is. I try to sit back and snipe when I can, and the Scope's extra range is nice for that, but enemies inevitably reach me, or I try going after them, which is where the real reason I use the E-Liter comes into play: Burst Bombs. I always put on a Damage Up or two so these will do a lot of damage with each hit, letting me be decently threatening in close combat (where I inevitably end up, either because enemies found me or I jumped down into the fray). Echolocator is also alright, primarily for the instant refill. I still don't feel comfortable playing a Charger (my instincts keep telling me to go closer, but sniping is best done from a distance where I won't get wrecked for missing), and my aim is shaky at times, but I still like the E-Liter.
Fourth is the N-Zap '89. I wrecked everyone during Splatfest with it, but after that I mostly forgot about it in favor of other weapons. However, I picked it back up today, and I'm really feeling it again! Sprinkler/Inkstrike with a Special Charge Up or two is an amazing loadout for getting lots of useful Inkstrikes, and the range on it's pretty neat too. Its rapid-fire is a bit linear (seriously, it's practically a straight line), which isn't good when your aim is as shaky as mine is, but other than that (and rusty-ness, it's been a while since I kinda dropped it) it's a good weapon.
And finally, the .52 Gal Deco. I used to love this thing; it has power, range, Seekers for getting around fairly quickly (or shooting at faraway enemies like you're supposed to) and Inkstrikes, which are always nice, but it fires fairly slowly. Over time, I switched over to other weapons, leaving the Deco behind, but I've come back to it and it's still good. Still kinda rusty with it though.
As for tertiaries, I suppose the Tentatek Splattershot (it's good, I just don't like how it feels), Krak-On Splat Roller (Octobrush pretty much has it beat to me, but occasionally I retry it), Splash-O-Matic (it's alright, mostly for Suction Bomb Rush, used to like it more), Inkbrush (Sprinkler/Inkstrike with SONIC SPEED, but not a good weapon for attacking because it has no range (requiring me to get up in people's faces to hurt them so I don't use it much), Splatterscope (I like Splat Bomb Rush, but other than that I feel like I'm playing a faster-charging E-Liter with a bit less range and worse close-range options), Aerospray RG (it feels nice, especially in Turf War, and is surprisingly decent in Ranked, but I hate the lack of range (fire speed mitigates its low power to me) and am not a big fan of Ink Mines), Splattershot Jr. (I like its well-roundedness, but the short range and low power hurts it for me) and Carbon Roller (it's like a slower Inkbrush that has Roller power and ranged attacks, but it's still not quite quick enough and its short range means the Splat and Gold Dynamo Rollers leave it in the dust).