For me it's a tie between ghost, fighting and grass.
Grass because I usually like support/tank roles in games even though it's not the best typing for that, although it's also because I like combinations of nature+something for some reason, especially if they are in contrast a lot (such as grass/steel).
Ghost because awesome colors, awesome designs overall and because I'm a fan of the horror and the 2spooky in general.
Fighting I'm not sure why, back in RBY I thought I hated that typing because all I saw was the machop line which I think is terrible to this day, but then I fell in love with Hitmonlee. And Breelom. And my favorite pokemon of all, Toxicroak. It's just that I like very specific fighting pokemons.
So far I was very pleased with the two Grass/Fighting pokes and the Ghost/Grass one, now I eagerly await for a Ghost/Fighting.
honorable mentions: ice and ground, but mamoswine a shit
