Well might as well make a post now that I've been brought up and a proper post from me is overdue. (Though I was referring to how Kyon cannot fathom people not having Mario as one of their favorites.)
I have a fondness for Toadette that I've brough up several times before and I guess I might as well explain myself for once. The Gamecube era was when I first really got into gaming and while I was familiar with most of the Mario cast previously, Toadette was a new character for the era and struck a cord with me since appearing in many games that I really enjoyed from that time like Mario Kart Double Dash and Paper Mario The Thousand Year Door and has since been a personal favorite of mine.
Another character that has left an impact on me is Samus. I don't feel the need to explain her so I'll just say that the Metroid series has long been a series that I have had a keen interest in but when I was young was intimidated by how difficult I found Metroid Prime. I wouldn't return to it until I found myself ready to take it on.
As for lesser characters,
For the longest time I never thought much of Princess Peach but lately has grown on me after my brief interest in actually becoming better at Smash Bros and although I've given up on that I still like her.
I also really like Roy for being cool and having amazing voice acting and not annoying like Funky Kong.