I remember I used to want to get good with Slosher, Octobrush and rollers, but had a hard time clicking with the weapons, but if I try the weapon enough I usually don't have much trouble liking it! Slosher has been one of my favorite main weapons for a while even.
The current weapon I do have problems with is pencil, mostly because I feel the comps I get on solo Q are really wack, or catch myself blaming my teammates more than I should since I have yet to get used to the main weapon to impact fights as much as it potentially could.
Had the same trouble with foil flingza for a while, in which the comps I was in were lacking because I thought the weapon was more of a mid range sitting back spamming bombs and was mostly paired with backlines, but as of right now I feel I get the weapon more, even if I don't hit all my vertical flicks as I would like, I really like it, I played it for a bit until I got used to it and now it's a weapon I really like!
I honestly feel I could like any weapon as long as I give it enough time, which is why I have a hard time thinking of my best weapon hahhah, the variety of the weapons is a big part on why I love playing Splatoon so much, I feel like I could learn any weapon! I will always praise the variety and uniqueness of almost every single weapon in this game, even if kits hold some weapons so much...
That being said, that's for weapons I feel like giving a try, there are some I'm simply not interested in, but that's another thing.