I absolutely love Lubba :') Some other favorites include Monty Mole, Birdo, and Waluigi. In terms of playing though, I usually like to pick Peach or Daisy.
I love Luigi and Toadette. I also really like picking Dry Bones in games where he’s available.
I think Super Mario Bros. Wonder had a great roster of playable characters for a main line game in this way, I played as all of the available characters at some point during my play through!
Princess Daisy, Toadette and Pauline. Every game they're in I'll play them as. (Except in Mario Kart 8. I don't like how Daisy acts in that game and Toadette is unviable. I'll be my Male Villager thank you, which that reason alone is why I don't play as Pauline online either...)
Not to worry, Super Mario Bros Wonder and Super Mario Party Jamboree will have me play as both Daisy and Toadette. Pauline as well!
King Boo! I've always loved the boos, and his little crown is the perfect finishing touch.
I definitely prefer the enemies, and some of the more creature-looking characters. Other favorites would be Chain Chomps, Piranha Plants, Dry Bones, Bloopers, and Toad/Toadette.
I don't think I would've been able to think of 5 Mario characters quickly off the bat had I not scrolled before posting lol I'll just say Mario for the SSB4 days