My answer won't be very good, cos I tend to find a character I like on each side, then try and get fairly decent with them before trying others, so I've only really played 2 characters for a reasonable amount of time.
Plants - Sunflower
With the right perks equipped, the amount of healing that she can churn out is really high. I only get a handful of kills per game at the most, but then I'm not trying to get kills. It is frustrating that nobody really talks in the game, cos Sunflower's laser beam attack could be super powerful if a tank player put up a shield in front of me while I'm doing it, but that sort of thing never happens, so using it is usually a death sentence unfortunately. Her primary fire is weak, but I think it should be, cos she's not supposed to be a character you play offensively.
Zombies - Captain Deadbeard
Given how hectic this game can be, with so many players on each side, I find him to be super strong. A fully charged shot with his primary weapon does a ton of damage. You can get to higher ground easily. The explosive barrel ability can be used both offensively and defensively, although the range is not great. The parrot's mobility is a bit limited, but then I think it needs to be given how strong the secondary fire is. The only thing I don't like is that close up, his primary fire when not aiming down sights feels like it does next to nothing.
