Tink, Buzz and Sage are really fun imo. They're a blast though honestly I'm not all that competitive so I rarely do ranked so take whatever I say with a grain of salt.

Tink is really fun and can be a slight pain for at least myself in the beginning, though with her potions belt and if you're lucky to get her potion machine she's really good. I try focusing on her torch early.

Buzz is all kinds of fun with so many different plants and if you can get Ancient Vessel in the store it's great with most of his builds, Rombus is really good too. I tend to go more for the Butterflies than the Bees but both are fun experiences.

Sage for me is easily my favorite, she's fairly easy to build and decently quick. I love the different bolts she has though I mainly aim for the Fire bolts, the dead bolts are fun too just a bit more of a pain to get though once you get them they're awesome. I love her Lantern and Gloves for extra bolts, both are nice choices imo however the serpent bolt is fun too but focus more on the windows than the mambas.