My favorite characters are Ashley (for obvious reasons) and Lulu, she's too adorable in her little cutscenes ("If I'm gonna face Wario... I gotta carb up!"). In the past though I had a thing for Orbulon and Dribble & Spitz. It's a shame there wasn't a new vocal song in their new stage.
As a matter of fact, my favourite WarioWare character (besides Wario himself of course) happens to be Dr. Crygor. In the past, I used to be more fond of Jimmy T. and Mona, and although I still really like them, I'm more on the Dr. Crygor side by now.
Ashley is still my fav even if some unfortunate interractions with others (not Kyon in case he feels the comment is aimed at him) and the Smash tantrums did a number on my fondness for the character, lol.
Sorry, Cryg. Orby is my baby boi. His looks are super cute, and he's so adorbs with that curiosity and clumsiness and stuff, and he can kinda be a bad lil boi, almost like Ashley but wanting to be an alien invader instead of a witch, but unlike her he actually seems to have more of an "innocent demeanor" than her, and he doesn't want to destroy anybody like she would. Also, he doesn't want his smooth skin touched! Maybe Ashley wouldn't want to be touched either! But he wouldn't toast or brew, he'd just teleport. He should definitely have a reign of terror like she did because he's sorta like a More-Adorable-Alien-Ashley.
I'm more of a Jimmy T type of guy because he reminds me of Miror B. from Pokémon and Body Rock and Cold Wind are my favorite tracks in DIY related to him (the only Warioware game I played).