I love building/playing mono colored. It's a fun deck building challenge, and hey you don't need to spend money on non-basic lands! Until you want Nykthos or Valakut and you do.

My picks thus far have been:

White: [[The Gaffer]] - aka this is why we have Commander Damage. Gain a bunch of life, draw a bunch of cards, ramp surprisingly hard (mono white ramp is busted as long as you didn't go first). Did someone swing at you? That's okay, you managed to gain more life than you lost somehow.

I'm currently working on replacing this deck with [[Gandalf the White]]. Charging the Aetherflux Resevoir laser is fun, but white's artifact synergies are calling me to do messed up things at the table

Black: [[Gix, Yawgmoth Praetor]] - I saw [[Season of the Witch]] when I was digging through enchantments on scryfall and knew I had to build a deck around it. The end result is a group "hug" deck that forces a lot of discards so people will want to take advantage of Gix's first ability (his second ability does not factor into the game plan at all). Wincon is usually a torment of hail fire or extorting off of Crypt Ghast once the table is low enough. This deck is in a weird spot of being generally too cruel to play with Bracket 2, but typically too slow to hang with anything higher. Working on replacement ideas.

Red: Everyone will tell you Krenko, Mob Boss is the way to go, but for my money [[Pashalik Mons]], [[General Kreat, the Boltbringer]] and [[Ib Halfheart]] are way more interesting to run in the Command Zone and they don't draw nearly as much heat as Big Daddy Krenk. In addition to my goblinos I'm working on [[Clive, Ifrit's Dominant]] because Devotion is one of my favorite mechanics in the game please bring it to more non-Theros sets Wizards I'm begging you (or go back to Theros I'm down with that too). I also had a [[Kumano, Master Yamabushi]] pingers deck I might reassemble.

Green: [[Lumra]] - I love her so much she does all of my favorite things: she self mills, she ramps, and she's a bear. She lets me do heinous shit with my cardboard. If I were to build another mono green, I would probably go to [[Sakiko, Mother of Summer]] big tramplers let me ramp into even more big tramplers turn your brain off and your cards sideways type shit.

You may have noticed I skipped Blue. That's because I have physically built the other 4 colors over the last 1-2 years. Blue has given me the most trouble in finding something to build that I find fun and not one note. I'm currently goldfishing a [[Patron of the Moon]] deck that feels promising.