1.
His kit just fits how I play. I love AD bruisers, and I love sustain. He has a really cool buff/debuff based play style, that while relatively simple, has a lot of nuance that allows for some pretty epic plays, like blocking a 5 man charge with a Pillar, murdering a tower with your AD and AS steroids, and doing the Troll dance over you enemies' corpses. He hard counters a lot of champions really well, and can adapt to a ton of situations, because of how flexible his kit is. He is also one of, if not the strongest duelists of any bruiser in the game, again because of his numerous rebuffs and steroids.
2.
Poppy was a champ that I got that basically every smurf that played alongside me told me was a n00b trap when I first was starting out, and sometimes they were right. Most times though, I hard carried and 1v5ed the enemy team with over 20 kills at the end of the game. Hard to play, but her football tackle just makes me laugh every time I use it.
3.
I don't play ADC very often, but when I do, Corki is my absolute favorite. He is just incredibly fun to use, and combines some of my favorite attributes of ADCs into one champion. is both very safe and poke heavy, but can dive in and burst people at the drop of a hat. His mixed damage output makes him hard to counter, and his Moustache is just so epic in proportion that I feel obligated to play him.
Honorable Mentions
He was one of the first champions I picked up, and I love it when the enemy actually chases me because of how mad they get at me. He scales really hard into late game, and if he can get a bit ahead, he becomes an uncatchable move speed fiend a la Hecarim or Rammus. He has a simpler kit, but has enough strategic depth to still be really fun.
After his rework, he is one of my top picks because of how fun he is. The only reason he isn't one of my top three is that if the enemy knows how to avoid his abilities and escape his passive, life becomes really miserable for him.
I just started really playing him recently because of how good he is in the jungle, but he is starting to really grow on me. Getting a perfect combo off onto a laner (E-Q-W) is so satisfying, because you can usually melt at least 60% of their HP. Lategame, getting a perfect ult is ridiculous, and usually kills at least two people without any help from you team.
I really love the Idea of a steampunk cyborg, and on top of that he also throws in my other favorite qualities of being a burst mage. His augmentations make him feel like he is making significant profess throughout the game. The rework they gave him made him a lot better, the only problem being that the removal of the burn on his E made my favorite Rylai's Liandry's build pretty pointless on him.
Dishonorable Mentions (The least fun ones)
Strong or not, WW is just the least fun champion to play in my opinion.
ever since the rework, he just hasn't felt the same to me.
No matter how well I play him, or how fed I get, he never feels like he has the amount of burst everyone claims he has, and feels like a one trick pony who dashes in, unloads his damage, and hope it was enough to kill the enemy.