Phelddagrif is my favorite commander as a character and I hate that its kind will never be a thing in magic again...
My favorite to play is The Ur-Dragon because dragon tribal is just something I really like to do for some reason and this is as true to dragon tribal as it gets, unlike Scion of the Ur-Dragon that act like its gonna be tribal but then it pins you down and shoves a combo in your face.
This is a tough question to answer, so I've kinda avoided answering it for a while. But I think that I finally have a way to answer this question; which commanders do I play that do the most fun stuff, that lends itself to a deck that isn't completely reliant on the Commander, but when the commander hits and sticks is enables some total shenanigans. There are three commanders that fits that bill for me; Ghave, Guru of Spores, Endrek Sahr, Master Breeder, and Wort, the Raidmother, but I think that Wort, the Raidmother leads to some of the funnest overall plays and game experiences with the sheer amount of shenanigans it enables so she would be my favorite. It also fuels what is essentially an aggro-combo deck, which is pretty unique archetype-wise among my various decks.
Jokes aside, I have found that two is the best amount of colors for me, because monocolor decks are too predictable and lacking when it comes to answering enemy problem cards, and I just can't afford the cards required to make an optimal mana base for three or more colors.
Thus, I've been focusing on bicolor decks, since those are the best-working compromise for me... And of course, being a huge fan of Ravnica and of stories set in Ravnica, this means that guild leaders, maze runners and other such legends tend to rank among my absolute favorite commanders.
Izoni has been giving me exceptional results lately, proving to be just the right mix of rock, reanimator and combo: this has earned her the distinction of being the first commander for whom I've created a 100% real deck, without any proxies (recent reprints of cards like Urborg, Phyrexian Tower/Altar, Life from the Loam and the likes certainly helped with that).
Niv-Mizzet is also a guy I've always loved, and the recent printing of his Parun incarnation, which is a straight upgrade from his Firemind incarnation, has motivated me to invest even more on him.
And then there's Aurelia, my absolute favorite guild leader in terms of looks, personality and role in the story... But sadly I can't build a decent deck for her to save my life.
I also wanted to give the new Emmara a try, but sadly I don't own many Selesnya-colored cards, and "just make a lot of tokens and turn them sideways" is not a particularly appealong wincon for me (yes, a former Edgar player just said that).
I can't wait for the next wave of guild kits, so that I can try my hand at something Simic. Orzhov and Rakdos too, those are two color combinations I'm particularly fond of, but so far no commander printed for either has truly caught my attention... Here's hoping for something exciting in the next Ravnica set.