1. Haunter: Second form of what was originally the only ghost pokemon. I grew a bit attached when I played the game as a kid. Ditto's a close second.

 2. Rotom: I'm not really a fan of the Legendaries since they always felt like cheating the game, but Rotom's possession factor was pretty fun.

 3. Ghost: Their move sets are closer to the sort of game play I enjoy. Putting enemies to sleep before sapping their HP, cutting your own hit points to harm them further, having your death force the enemy to go with you, it's a ton of gambits and workarounds in lieu of direct combat.

 4. Gen One bitches. The original Gold version was nice and all, but the first game wasn't trying as hard as the others. It was a shot in the dark that lead to great success, and much of the story was campy and strange from being a first attempt. With each game following the first, you see the writers trying to be a little too serious progressively.

 5. Kanto, for it's glitches and GLITCH CITY. The layout was also simpler and more charming, while the newer ones are trying to be all about stuff like "HOLY SHIT THE WATER REFLECTS YOUR DUDE ON IT!"

 6. Team Rocket. I have a shirt for it, and the other groups weren't as blatantly about crime. They're also one of the few willing to go as far as to use a gun. The Manga's Pro-Team Rocket Lt. Surge appropriates them into badass weapons: A gun that shoots Electrodes and Voltorbs, Magneton on his shoulders to provide a defensive barrier, and a Zapdos on his back to power it all.

 7. "I am Agatha of the Elite Four! Oak's taken a lot of interest in you, child! That old duff was once tough and handsome! That was decades ago! Now he just wants to fiddle with his Pokédex! He's wrong! Pokémon are for fighting! [NAME]! I'll show you how a real trainer fights!" She insults the man who won't let you ride a bike indoors, then fights with dead Pokemon after talking about how it's all about fighting.

 8. James. The show mostly sucks beyond hindsight humor, but his English voice acting and moments of fail makes me laugh.

 9. As a victim of raw nostalgia, the first battle theme will always draw me in more than the others. Pokemon has had an amazing music team across their games (for example, check their gym themes, champion themes, legendary themes, rival themes, map music, etc), consistently being one of the more immersive parts of the game as a whole, but the first battle theme if I hear it will basically lure me to the source.

Edit: Huh, they slowed down the Cinnabar Island music for the later game when it was hit with an eruption. I love little things like that. Go figure it'd be the island MissingNo can be found on that'd become destroyed. Pre-Eruption - Post-Eruption.

10. Whichever one was that shitty one with Entei in it. I hate the movies for Pokemon (other than some of the art), but at least that one has the memory of making out with someone with some dry humping on the couch as an association with it.

11. I just play for fun and the torture of the opponent. I've become somewhat into EVs, but I am a big fan of Nuzlocke Challenges.

12. NIGHTMARE FUEL! (Unnerving Pokedex entries are the best part).

I miss the glory days of Twitch Plays Pokemon, and the glory of Digrat. Friends of mine still play the games and tend to poke me with a stick from time to time to nudge me into going along with them.