King DeDeDe is my favourite Kirby character because he is the token big brawler and has a badass weapon. Also his coat is very beautiful.
My favourite design is the Smash Bros Ultimate design. The GBA and DS designs are great too. I do not like the DS and Switch designs.
However, I like Bowser more than deDeDE because he is more connected to my childhood memories. I played a lot of Mario and he was basically in every single Mario game. I especially enjoyed the Mario & Luigi series titles.

When it comes to adult games, I have a lesser connection to the characters mostly because every character only appears in one or two games and the casts tend to get switched between games. However I like Dogmeat. Taurus demon is my favourite Dark Souls boss, but since he only appears about 5 times through the game, I have a much lesser connection to him than bowser. Orcs from Dragon quest also hold a small amount of sentimential value to me.