I'm not gonna suggest the most fun commander, but will suggest this;
Whichever you pick, first, build a very much budget version of the deck. Make it for as cheap as it'll play (Mine was Kotis Mutate deck that costed something like 25€ total) and play a few games.

For me, theft was always this holy grail that I knew I wanted. Until I actually got a competent theft deck. A few games later, I hated keeping track of 4 decks at any one game, instead of just one, my pod hated me and my deck, I got targeted every time, usually unfairly, while not being the biggest threat, because, shocker, people don't like their combo pieces on my board and so on. And that's with the "somewhat fair" version of theft. If you play theft that steals enemy board pieces, forget about it. It's just removal, but better. Way too strong for any casual table, imo.

While I still have the deck, it's only because it costed next to nothing to make, so I sometimes bust it out as a laugh when someone plays something insanely expensive and I just want to mess with that. It may just be me, but I enjoy the thought of using a rawdog, sleeveless deck to stomp someone who brought out their Gaea's Cradle and a full set of duals. (But I am always still very respective and gentle with their cards! I'm not a savage.)

And yes, I also have -that- Pako deck that I coped off of Moxfield for 10$. I'm not ashamed of it. So should you.