well in the comic books, their are more than the new udon series, ryu shows great ablilty and is treated as the single most deadly fighter.
also if i where to go off the mortal kombat cartoon series, vs the street fighter cartoons " their are many sf cartoon series too" ryu ablilty far out shines lui kang's.
even in the video games :ie sf, sfIII thrid strike, sf ahpla, marvel vs campom, ryu tech(game moves ablilty) seems to defeat and this is without adding in evil ryu.
i hope this explains what my earlier statment; that base of all I have seen in these things lui kang would not come close.
Ryu, hands down. Having the ability to turn into a dragon and emit fire in balls from your hands is nice and all, but when your opponent can unleash powerful energy blasts/waves from a distance, plan on getting Hadouken'd into a wall, with your body writhing in pain. Besides them being similar in that they've fought tougher, more powerful enemies, Ryu has it in the bag with his fighting Akuma (who'd be a better match toward anyone in the MK universe).