Favorite to use is H-3 Nozzlenose. Least favorite to use is probably Splattershot Jr..
I like my weapons to be accurate. I really like my weapons to be precise. H-3 is very much both. Additionally, no weapon sound is more satisfying than the one produced by a three-shot direct. L-3 and Tri-Stringer are both not far behind, though they definitely lack in kits.
Splattershot Jr. spams bombs, and then spams more bombs. Then it activates its special to instantly refill its ink tank, and proceeds to spam yet more bombs. If I want to coat the stage in paint and explosives, I'll pick Wellstring. Splattershot and N-ZAP are similarly boring.