When I started playing the old school Pokémon games, I began with Pokémon Yellow. I kind of feel bad for it now, but back then, I didn't use the Pikachu that I started with because I wasn't a fan of Pikachu in-game at the time. I liked Ash's Pikachu a lot though when watching the show. Because I played Pokémon Yellow, I didn't have just one starter Pokémon, meaning that I had experience with all three because Bulbasaur, Squirtle, and Charmander were given to you as gifts throughout certain points of the game. Because each of them have their own charm and usefulness, it's hard for me to pick a surefire favorite, at least at that time. In other words, I loved Bulbasaur because it was a great Pokémon for an in-game playthrough at the time, being able to destroy Brock and Misty early on, and resist Lt. Surge. Squirtle was great when you needed a Pokémon to help you Surf as you got farther into the game. Charmander was challenging to use early on, but when you got it to evolve, you had a reliable and strong Pokémon that could learn Fly and help you fast travel. It was hard to pick a favorite because they were all so good.
Nowadays, I select Bulbasaur as my favorite because it evolves into Venasaur, which can do some great things in battle that would make it a mainstay in nearly every game it's featured in. Yet, I don't think the Bulbasaur line gets much love from the fans at least compared to the other, especially Charizard. As for Kanto and Johto, it's hard to choose which one I liked the best. Many people say Kanto was too plain, but I kind of disagree. In my opinion, it's better than Sinnoh, which I thought didn't really have too much landmarks to make it stand out. Ever noticed how many people say Hoenn had "too much water?" Well, I believe Sinnoh had too much woods. However, Kanto had big modern cities such as Celadon, Saffron, Vermillion, Fuchsia and its Safari Zone, and so on. Johto had a more traditional Japanese feel to it, which was especially evident in places such as Violet City and Ecruteak City, which was really nice. It's like Kanto and Johto directly contrasted to each other. I also have to appreciate the Johto games for improving upon generation I and adding the many features in Pokémon that we know and love today.