Toughest Street Fighter characters in Fighting Games?

This question is slightly different now, as it is about characters than games.

The question is which Street Fighter characters are the hardest/toughest characters that none of the characters from other fighting games like Tekken or Mortal Kombat might be able to beat easily?

I would consider Street Fighter characters M.Bison and Ryu in my opinion. As I have said before, although M.Bison has quite similar moves to Mortal Kombat's Raiden and Ryu has quite similar moves to Tekken's Kazuya, they are just so hard that Street Fighter games are very tough games though interesting games.

Kazuya and Raiden are easy as pie to beat in their games, but Ryu and M.Bison is not. Just sometimes get insane when playing and losing to them over and over again in Street Fighter because of their psycho power and hadoukens/shoryukens.

Can I also get anymore of others responses on this question that is:

"Which Street Fighter characters are the toughest/hardest characters that none of the characters from other fighting games like Tekken or Mortal Kombat might be able to beat easily?"

Please answer, please! Which Street Fighter Characters are the toughest for other fighting games?

Ok, super earnest answer for kinda bizarre thread... ready?

ST Akuma stands out mostly because of how busted he was design-wise. Especially when you consider that MK and Tekken are games that are designed around the idea of taking turns, Akuma could just pressure relentlessly and never have to worry about it.

By a similar token, C.Viper from UMvC3 is just so bananas in terms of mobility and options, if you just transplanted her into any MK or Tekken game she would be flying circles around every character, blowing them up at will.

3S Chun beats up everybody. None of them survive in games with air dashes though.

Sorry, we don't really allow this sort of "battle thread" here on Giant Bomb. These hypothetical discussions of character x vs. character y tend to only lead to bickering and arguing about things with no discernible answer.