This is my tier list, (opinion)
S tier (everything that is currently OP): Z7 Imp, Electro Citron A+ tier (Borderline Op char that probably should get a nerf) : None A tier (Strong char that might need a nerf) : Plasma Pea, Future cactus, Paleontologist, Camo ranger, BBQ corn A- tier (Strong char that may need a nerf in the future but aren't a problem right now) : Computer scientist, Mechanic, Basic corn, Marine biologist, Basic Soldier, Basic Citron, Basic Imp, Ice Citron, Agent Pea, Law Pea, Captain Cannon, Electro Pea, Petrified Cactus, Pylon imp, Drake imp B+ tier (Strong char,but don't need any major change right now) : Basic Scientist, Zoologist, Chemist, Stuffy flower, Landscaper, Sanitation Expert,Vampire flower, Scuba soldier, Captain Deadbeard, Electro pea, Armor chomper, Tennis star, Frost rose, Basic Cactus, Mystic flower, Power cactus, Basic Rose B tier (Balanced,aim to get in here I guess) : Super Commando, Fire cactus, Metal petal, Basic All-star, Peashooter, Toxic Pea, Sun pharaoh, Sunflower, Shadow flower, Fire flower, Fire chomper, Power chomper, Welder, Hot rod Chomper , Cricket star, Ice pea, Dr toxic, Baseball star, Golf star, Druid rose, Mob cob, Roadie Z, AC perry, SHRIMP, Basic Superbrain, Cosmic brain, Electrobrain, Toxic citron, Astronaut, Arctic trooper, Toxic brain, Centurion, Park ranger, Plumber B- tier (Weak char,but probably don't need any major buff for the meantime) : Engineer, Painter, Alien flower, Fire Pea, Power Flower, Goalie star, Moto-x-star, Yeti chomper, Pop corn, Rock pea, General supremo, Sky trooper, Captain Sharkbite, Electrician, Fire rose, Camo cactus, Count chompula (C), Physicist, Party Imp (C) C+ tier (Weak char that do fine right now but could use a buff) : Chomper, Ice cactus, Bandit cactus, Zen cactus, Captain Partyman, Disco chomper, Party corn, Jade Cactus, Commando Pea, Unicorn chomper C tier (Weak char that need buff): Archaeologist, Party brain, Party citron, Party rose, Captain Flameface, Breakfast brain C- tier (Weaker char that need a buff to be viable): Tank commander, Toxic Chomper, Chomp thing, Wresting star D tier (trash stuff that you have no reason to use or are completely outclassed at what they do): Hockey star, Rugby star