My opinions. I'm not good at intros.
The 15 Best
There are a lot (A LOT) of plants. Each with their own capability. Some excell, some fail. These are the ones that excell.
Tall-nut may be one of the least interesting plants, but it's exceptionally useful. Its utility is most apparent in Plants vs. Zombies, where it is the strongest defensive plant, and the one sole thing that can dependably stop all vaulters. Each one has specific Tall-nut-free strategies, but it makes life easier. In the sequel, it's made less practical by the Infi-nut, a later entry. It's still very helpful against things like Bulls, though.
Often considered the "weakest" pult, Kernel-pult is actually extremely deadly. If you don't think this now, you will after two to three Kernel-pults butter-lock a strong zombie to death. Like the Tall-nut, it's a bit better in the original, but is still no slouch in the sequel; in fact, it outclasses the Cabbage-pult EVEN MORE in the sequel, mostly due to Plant Food.
#13: Gatling Pea
A plant only seen in the original, this plant is a powerhouse. Its sheer danger is mitigated slightly by its high cost and slow recharge, but for regular Survival and some Survival: Hard levels, its power is very beneficial. It's not too helpful in Survival: Endless, but it's still very useful otherwise. Honestly, the sequel could use this plant, more than it needed the Pea Pod.
I might get hate for this. The Blover is actually quite powerful, even when not used in the semi-cheaty Spring Blover strategy. Like the Tall-nut and Kernel-pult, it is more useful in the original game, but still useful in the sequel. It outclasses the Cactus by far, with the Cattail being its only competition, making Blover usually the better option. Plus, it clears fog, something that the Plantern does less efficiently.
Why is the strongest instant kill of them all #11? Because it has two major drawbacks that hinder its utility - it's a mushroom, and it leaves a crater. If it weren't for these, it'd be the most perfect instant imaginable.
#10: Umbrella Leaf
An oft underestimated plant, the Umbrella Leaf is the third most vital plant for roof levels. That excludes the Sunflower, since it's not specifically vital for a level set. The first most vital's the Flower Pot, and the second's the Cabbage-pult; Bungees are tough to take down without reflecting them in general.
#9: Bonk Choy
This plant gets more hate than it deserves. It far outclasses both earlier plants similar to it - the Chomper and the Beet. It's very powerful early on, and is still somewhat viable later on with good support. It's not perfect, but more than useful enough for standard levels.
A superior plant to the Bonk Choy is the Snapdragon. Unlike the Bonk Choy, the Snapdragon can take down 2 zombies in other lanes at the same time; a column defeats the largest charges of Jetpack Zombies; two columns are a death sentence for most zombies. One alone isn't too strong, but the more you have, the stronger they all are.
Like the Snapdragon and the Lightning Reed, a plant that almost made the cut, Starfruit have power in numbers. One Starfruit is pathetic. Two aren't much better. But two to three full columns? Not much will have a chance, and what does, you have defensive plants and Spikeweed/Spikerock. Some things will survive quite readily, but those scenarios aren't too common.
While not the best plant in the original, the Fume-shroom takes its ability to a whole new level in the sequel. Instead of dealing average damage to a crowd, it now deals twice as much damage as normal to a crowd. Its sole disadvantage is its short range, but that's what you have things like Melon-pults for. After the Fume-shroom, we get to the Top 5.
#5: Twin Sunflower
Ah yes, the Twin Sunflower. Hands-down a great sun producer, although, like the Gatling Pea, its utility was mitigated by its status as an upgrade. In the sequel, however, it's extremely useful, especially after getting the starting sun boost. You get it during Ancient Egypt, and can have it before going to Pirate Seas if your persistent. Recently, it was outclassed by the Sun-shroom, but its severely mediocre status in the original negates its massive utility in the sequel.
Like the Twin Sunflower and Gatling Pea, this plant wasn't especially useful in normal levels in the original. However, in the sequel, where it shed its upgrade status, it became king. Useful in nearly every scenario, this plant is among the best. Its only drawback is that it takes 3 hits instead of 9.
Infi-nut is, hands-down, the best defensive plant. It has theoretically infinite health, and its Plant Food is one of the best. There's not really much to say about this plant.
Hands-down THE BEST mushroom. This one's fairly obvious, actually.
#1: Winter Melon
I doubt I need to explain this.
The 15 Worst