Yoshi (as if you didn't know): Ever since playing a Mario game for the first time (Mario Kart Super Circuit), I have always thought that Yoshi was the most adorable creature ever, with the sweetest little voice.
Daisy: Mario Kart Double Dash was my first impression of Daisy. I know what you're thinking, that would make it odd for me to be a Daisy fan. Honestly, I didn't think she said "Hi I'm Daisy" all that much or that loudly, especially not to the levels the internet would have you believe. What I liked most about Daisy is how cheerful she is, which showed in her 2nd/3rd place voice clip in MKDD: "Not too bad, right?" I do wish we could see more of Sarasaland and the people there. Maybe Daisy could act as a supporting character, giving tips about her kingdom if you ask her.
Toad: He's just a loyal and stand-up little guy. Plus, he starred in Wario's Woods, marking him as a hero.
Baby Daisy: They took Daisy and made her into a cute little baby. Nuff said, I'd say.
Bowser: I love his one-liners. What can I say? He's Bowser, baby!
Koopalings & Bowser Jr.: I don't care what canon says. They're all Bowser's kids. I have them at the same rank on my overall list of favorite Mario characters, but I also have them ranked by favorites within their own group.
Pauline: Pauline didn't really register on my radar that much. She was just one of those characters who's just... there. It wasn't until I introduced her into my fanfic as a member of the supporting cast that I starting liking her. She hasn't had much revealed about her personality in the games, which means I can write her in any way so long as it lines up to what little we do know about her. If she did appear in more games, she'd be able to get more fleshed out, and maybe get an official voice (aside from the uncredited role someone made for her in Mario vs. Donkey Kong: Mini-land Mayhem).
Rosalina: Instead of doing the whole "backstory/Mercedes Rose" song and dance that people always do, I'm going to talk about the character development she seems to have gotten. She said she would come back to her home planet once every 100 years. I have no reason to doubt that she kept up that tradition. But I think once she met and befriended Mario and co., she decided to come back more frequently. Friendship is a wonderful thing. Friendship is Magic
Mario & Luigi: I have the Bros. tied. I'm the younger of two brothers myself (we're not twins, but we look enough alike that we might as well be). I just love how in sync the Mario Bros. are. Nothing can beat the dynamic duo of two (or more!) siblings. Shoutout to BLOF and LGM
Peach: She might be number 10 on my list, but I can't help but be in awe of this girl. In spite of the frequent kidnappings she has to put up with, she still maintains a pleasant and graceful demeanor in most situations. It's been established in previous games that she has a heart of "Incorruptible Pure Pureness," which is impressive. But I like that just because she's pure-hearted doesn't mean she's not competitive. It makes her more human.