Warusaki's CVS2 Ryu. If a character needs adjustments to scaling or something, I base it on CVS2 Ryu. And he seems to be a good character for testing hitstate results and such...

If I need to test beating up on a character, I'll use one of mine or something. I can tell if the AI is really bad or the character is weak if I can mow them down with any of my low-tier stuff.

Eventually, I might test AI vs AI, so I test against my Andore, CVS Violent Ken, and some others. If it's a crazy powerful character, I have some bosses for that.