This is purely my opinion, OK? Please no flame wars in the comments.
First, we'll start with the worst cards.
CannonI was originally planning to place Tesla here instead, but then I remembered: Tesla can attack air and is invincible when underground. The Cannon, on the other hand is so underpowered it made the list as the worst Common in the list. This card used to be good, but Supercell nerfed this card so heavily that it now sucks. Cannon needs some sort of buff to make it good again.
Barbarian HutIt's way too expensive and spawns Barbarians way too slow. Goblin Hut could have been here instead, but I personally find Barbarian Hut to be worse. Plus, Rocket can easily take care of the hut. It can be used to annoy people, but other than that this is probably the worst spawner in the game.
CloneIt's arguable that Mirror could also be here, but Clone's worse in my opinion. Zap can easily take care of it. Clone's only OP when you cloned a bunch of powerful units that are already hitting a tower.
SparkyShe is called Trash Can on Wheels for a reason. Supercell, instead of telling people to not call her Trash Can on Wheels buff her so that the majority will stop calling her that. Her charge time is way too slow and air troops can easily take her out. She's decent if supported, but without support she just sucks.
Now, we'll move on to the best cards.
ZapIt's quite versatile, great for taking out pesky swarms and is overall quite versatile. Zap is in all my decks and without it, my decks could be worse. Honestly, this card is great however very annoying. I'm not sure if this card should be nerfed or not. A nerf would kill it out of the meta and buff would make it even more popular.
GiantGiant may not have the best damage and speed, however he's a great meatshield for weaker units. He can be swarmed by Skeleton Army for a positive Elixir trade, however a Zap can take care of that. One could argue that Hog Rider has better speed and damage, however Hog simply doesn't fit my decks as good as Giant. Overall, these are all the reasons why Giant is the best Rare in my opinion.
GolemIt's quite slow, however it's quite tanky to make up for that. Golem decks are becoming the Meta, so this card's popularity is increasing. It's still vulnerable without support, but with it this card's a beast. I have a lot of other epics to choose from, however I picked Golem out of all of them. Only hard counter to this guy is the Inferno Tower.
The LogIt's a really good spell. Only for two Elixir, this spell can take out troops and knock back others. Perfect for taking out swarms and low health troops such as the Princess. All in all, this is probably the best Legendary in my opinion.
Post your opinion in the comments below!