Oh, right. I was just mentioning Solaris because Mephiles and Ilbis make up Solaris, but Mephiles alone would probably be more evil than Infinite.
Mephiles is the most evil and attempted more destruction, but Infinite is incredibly sadistic. I'd say it even outs. Infinite is on par with Black Doom and Erazor Djinn.
Mephiles.
I don't know,but I do know that Infinite IS THE EDGIEST!OW THE EDGE!
Debatably Dr. Robotnik. I know he is a silly fatman and he is entertaining but when he is serious he is very threatening surprisingly. In recent games it seems he is starting to become increasingly more and more threatening. In Unleashed he destroyed the world splitting it into pieces to awaken a demon in the planet's core to use it's power to create his own empire. In Colors he steals the lifeforce from innocent aliens to power a device that is capable of turning everyone on the planet into his zombie puppets. You get a small taste of it's power with Tails. In Generations he finds what I am assuming is the remains of Solaris, roboticizes it turning it into a mech then teams up with his past self and goes through time to try and undo every mistake he has made in the past. He is going so far as to mess around with time and space for his own selfish means. Lost World is debatable. He created an extraction device to steal the planet's energy. Zavok hijacks Robotnik's position becoming the big bad while Robotnik apparently teams up with Sonic. It is then revealed that Robotnik was merely using Sonic to defeat Zavok and his followers so he could use the extractor for himself outright betraying Sonic and becoming the actual final boss of the game. Forces is where he stoops to new levels of awful. Let's see. He recruits a mercenary, gives him a helmet and fuses him with a powerful illusionary gem that is capable of mass mind screwing, time space warping, and generating phantom entities. He then has said follower ruthlessly beat Sonic to near death, has him locked up in the Death Egg to be tortured and ejected into space, has his robots and Infinite cause wide spread destruction and supposedly kill countless innocents. Then to top it all off he goes so far as to drop an artificial sun on Sonic and when that fails uses a robot machine powered by the Phantom Ruby to outright destroy the resistance himself starting with Sonic. Gone are the simple comical looking badniks. You now have towering Death Egg Sentinels and a massive Death Crab robot. Smaller units now look cold, menacing and souless such as the common Egg Pawn. There is no trace of humanity left in old Egghead. He has stooped to whole new levels of awful in Forces. I never expected something like that in all honestly.
Now that I think about it the Sonic series has some really messed up antagonists.
This is only between Infinite and Mephiles the Dark; it has nothing to do with Dr. Robotnik.