In Splatoon 1 my favorites were the Slosher, 52. Gal, and Custom Dual Squelcher. I used them for zones, tc, and rainmaker respectively. I loved slosher for its ability to kill in the strangest of locations and how intuitive it was to play. 52. I used mostly when I needed some raw power and to deal with port mackerel. Custom dual was my favorite as it allowed for a hugely mobile playstyle that didn't sacrifice range from the main weapon.
In Splatoon 2 it's a little harder to say. I like Kensa 52. because it reminds me of 52 from Splat1. I would say I enjoy playing Octobrush and Hydra quite a bit in this game. Octobrush has that mobility that I find lacking on a lot of weapons in 2 (esp. Octoveau) And Custom hydra is just such a powerhouse and ink mines in its set allows it to be extra cheeky.