(I am aware there may be spelling and grammar mistakes.)
Peashooter: Sucks, don't use it except when you really have to.
Sunflower: Twin Sunflower is superior in almost any aspect, only use it until you get the choice to use Twin Sunflower.
Wall-nut: For holding off stuff while you still have to use Peashooter. Not worth a slot later on.
Potato Mine: Early killer that works on everything except Chicken Wrangler Zombies. Hard to use as the level advances.
Cabbage-pult: Sucks only slightly less than Peashooter but you actually have to get a card for it. Don't use it much.
Bloomerang: Weak and AoE starts becoming pathetic. But it's kind of acceptable for very early levels.
Iceberg Lettuce: Helpful for early level game and plant Food helps with late game. Can be used to ensure a Wild West Gargantuar death without it crushing anything.
Grave Buster: Useless but get its card so it doesn't bother you later.
Bonk Choy: Potential anti-chicken until you get the spike plants and Lightning Reed. Isn't very good against thrown Imps and specially bad against Wild West Gargantuars.
Repeater: Faster shooting no AoE somewhat stronger Bloomerang. Not much to say. Potential early shooter, but my strategies don't accomodate early shooters anymore.
Twin Sunflower: Best Ancient Egypt plant. This plant is essential to getting enough sun for Winter Melons, which are vital for getting far.
Kernel-pult: Weak, butter prefers to not help. Get its card so it doesn't bother you.
Snapdragon: Ok AoE plant, but has negative synergy with Winter Melon and Iceberg Lettuce.
Spikeweed: Anti-chicken when there are no Gargantuars.
Spring Bean: Unless you're going with Bean Plant Food+Blover, don't use it other then getting its card so it doesn't bother you latter.
Coconut Cannon: Haven't found much of a use for this guy since it's so expensive and only so helpful. Minecarts?
Threepeater: Three Peashooters so it sucks. Get its card so it doesn't bother you later.
Spikerock: To ensure death of Wild West Gargantuar-thrown Zombie Bull Riders and anti-Chicken in Wild West Gargantuar levels with Chicken Wrangler Zombies.
Cherry Bomb: Damage Wild West Gargantuars and kill Zombie Bulls. Best Pirate Seas plant.
Split Pea: Anti-Prospector when Spikerock and Spikeweed are unavailable, along with Blover and Iceberg Lettuce?
Chili Bean: Early zombie killer when given the opportunity. But sometimes it's not worth the slot.
Pea Pod: Minecarts, not much better than individual Peashooters. I kinda like it though.
Lightning Reed: Auxiliary anti-chicken during early level, replace with a column of Spike plants up front.
Melon-pult: To add damage after 1 column of Winter Melons is built. Not completely necessary so don't sacrifice a slot for it if unneeded.
Tall-nut: Defends you against many things, including Zombie Bull Riders from Zombie Bulls. Prevents Lawn Mower triggers, so it's nice.
Winter Melon: Best Wild West plant. High damage and slows down zombies. Vital to beat anything. Especially Wild West Gargantuars.
Laser Bean: You need all the space you can get, and it's unpromising damage output doesn't help it. Fires too slow to be Anti-Chicken or Anti-Prospector.
Blover: Best support plant? Blows away Bull Riders and Prospectors mid-air but beware some distance will happen from Bull Riders so they may still trigger Lawn Mowers. Spring Bean Plant Food+Blover=Massacre.
Citron: I just plain don't get it; you fill this.
E.M.Peach: Only useful on Zombie Bull, not worth a slot. Iceberg Lettuce is better here.
Infi-nut: Takes a slot and doesn't promise much back. Can be jumped by Bulls and can't take much damage; so, sorry if you thought I'd complement it here, but you were wrong.
Magnifying Grass: I don't get it either. Poncho Zombie bug in which it can kill a Poncho Zombie with a metal grate in one shot as long as it still has its poncho, I guess.
Tile Turnip: Nice, but you need all slots to be as efficiently used as possible.
Cowboy Zombie: No threat
Conehead Cowboy Zombie: Slight threat if you have only a column of Lightning Reeds.
Buckethead Cowboy Zombie: Consider it a threat until you have Winter Melons. Especially with Pianist Zombies.
Prospector Zombie: Annoying, jumps behind your defenses and destroys your hard work. Blover's recharge may be the difference between a successful jump and a fail. Spikerock at the very back/front?
Poncho Zombie: Not much more than Buckethead except for appearing more often.
Pianist Zombie: Annoying. Causes Bucketheads to change lanes and miss your Potato Mine. Kill quickly.
Wild West Gargantuar: Strong, can be delayed with minecarts, but not if they're not to your favor. If any of the back three columns have minecarts and there are Gargantuars, don't try to fight it and just get another layout with either the App Restart Trick or the Zen Garden Trick.
Zombie Bull Rider: Annoying hubbard that can trigger Lawn Mowers if you don't stop the Zombie Bull. And the sound effects are hella annoying.
Chicken Wrangler Zombie: Early spawner. Use Lightning Reeds early and THEN move to using Spikeweeds or Spikerocks.
Zombie Chicken: Triggers Lawn Mowers/Kills you if you have nothing against it. Lightning Reed early, Spikes late.
Zombie Bull: Really resistant and insists on appearing early. Use Tall-nuts, Cherry Bombs, Iceberg Lettuce, and any Potato Mines you may still have armed.
Zombot War Wagon: Doesn't appear. But it's a fun fight on WW-25.