Mine is definitely Hua Tuo, Honored Physician. I love decks with consistent value engines, and he's an interesting commander with less than 150 decks on scryfall.
Note: I tend to build budget decks because I am a poor student with a lot of debt, though the only expensive upgrades I can think of would be cards like Apex Devastator .
Sideboard is filled with cards that I haven previously had in the deck. Felt that pipers like howlpack piper and Champion of Rhonas are clunky because I generally want to be casting creatures from the top of my deck, not from my hand.
Besides the very unpopular Atraxa, praetor's voice (/s), I love my heartless hidetsugu deck. Commander burn is ... somewhat viable but delicious. Maddening hex, thermo-alchemist, guttersnipe, storm cards. It's all there!
I don't know if he's considered unpopular, but Chainer, Nightmare Adept is one of my all time favorite commanders, when he is leading rakdos dragons. Every card is a dragon, mentions dragons, or has dragons in the art. It is so slow and clunky, but I just love it. The main goal is to get Bladewing, The Risen onto the battlefield from the yard to cheat another dragon into play, to then bring Bladewing's Thrall back from the dead. It's stupid and not powerful, but it makes me feel warm and fuzzy inside.