For me, I'd have to say that, in order, my favorite types are..
1. Fire
Favorite Pokemon: Arcanine
I don't really know why, but ever since my second game I've had a strong preference for fire types, and I've only ever failed to put a fire type in my team for one game, Pokemon Diamond. Anyone who has played Diamond will probably know why this was the case, given I'm not a fan of monkeys. Hilariously, I actually strongly dislike intense heat, and prefer to be in colder climates. It's always easier to warm up than to cool down, after all. And yet, I guess I'm drawn by the warmth of the type,
like a moth to a flame. (Har har) Maybe I'm a pyromaniac? Or maybe I just enjoy the warm feeling of a good fire when it's cold out? Who knows. It definitely helps that fire types are usually very easy to locate.
2. Dark
Favorite Pokemon: Absol
I know you're probably thinking it. "Fire and Dark are your top two? You must like Houndoom!" ... Well yes,
yes I do, but there are plenty of other Pokemon of this type I like. Absol, Mightyena, Honchkrow, Umbreon, Hydreigon, the list is pretty big. I really enjoy the aesthetic of the majority of Dark types, They look tough, like they mean business, like they'll knock you out just for looking at 'em funny. The thing is, many Dark types are also
surprisingly soft-hearted. I can kinda relate. Without my glasses on I kinda have a scary face. Many years of ill fortune have basically etched a permanent scowl into my features, which my glasses partially hide. On the inside, though, I'm really sensitive and break really easily.
Another thing that I really enjoy about the Dark type is the fighting style. They're combat pragmatists. Dark type moves are full of secondary negative effects for the opponent, ranging from flinching to confusion to not being able to use items. Given my usual strategy is nothing more than charge in and throw out all the powerful moves, using a Dark type actually causes me to consider strategizing sometimes.
3. Electric
Favorite Pokemon: Luxray
Now this, right here? Wasn't always the case. Used to be Water type on account of my constant use of it. But, I have almost always raised an Electric type in every game too, and joining Team Instinct and gaining team pride kinda sealed the deal. On top of being good at stopping opponents from attacking with paralysis, most Electric types are quick on their feet, usually sacrificing defense for speed and power. This is also something I relate to, as while I can be pretty fast as needed, I've got next to no endurance to work with. One thing in particular that Electric types can do that brought them higher in my type fave list is actually how they're used in Pokemon Ranger, using their electricity to either power electrical objects or to recharge the Ranger's Capture Styler. Imagine how handy it'd be to be able to ask your electric type Pokemon to recharge a phone that's low on battery if you can't get to the next Pokemon Center in time to charge it normally! Of course, the better option would be to keep it charged, either by not using it actively or using a power bank. Not all Electric types are good at holding back their power after all.