I've never thought too much about my favorites, but if I had to sit down and rank franchises, Pokémon is far and away my #1. I've noticed over the years that I spend less time focused on game franchises and the like than I used to, and I suspect that's a natural progression. As that's happened, though, I've found myself opting to play Pokémon rather than playing other games. E.g., when I was 10 or so, I liked Pokémon better than other series, but I still spent a lot of time playing a bunch of other franchises. Now that I have less time for games, I've opted to cut out most of the franchises besides Pokémon (I still occasionally play Mario, Animal Crossing, and Zelda titles, but not that often), but I still play a lot of Pokémon.
When I was younger, I assumed that I would outgrow Pokémon. Apparently, that hasn't happened, and I'm happy with that. I'm sure that a bunch of Pokémon's appeal for me lies in its nostalgia value, and I'm not sure I'd try it today if I had never played it before, but as it is, I love the franchise. While I don't do as much with it as I sometimes did years ago (e.g., I don't watch new TV episodes anymore, though I still enjoy watching my Indigo League and Orange Island DVDs that I bought a couple of years ago), I still love Pokémon, and suspect that the franchise will always remain near to my heart.