That's a tough one. Majority of the characters I made were considered "filler" characters, but people fell in love with them too easily (even Handzy to the point where she offered to design them), and I ended up expanding them XD.

Ran out of ideas for filler characters to the point I had to recycle some from my scrapped RPG game. Savva was made using a combination of two characters (smart-ass middle-aged man and a depressed middle-aged man.) Polina was inspired by one of the female characters who is rich and rude (but Polina herself is less rude).

So, in short, I don't have a favorite one; but I treasure them all.