Females, as anyone with a brain would say, Nina wins. She's way stronger than any of the other girls bar none and wouldn't hesitate to kill. Anna would be a close second, but Nina would probably kill her too if she really tried.
Males, either Jin or Kazuya or Heihachi, obviously. Heihachi beat Kazuya in tekken 4 before losing to Jin, but Kazuya beat Heihachi in tekken 1. Plus Kazuya has the devil gene and can control it even better than Jin, so automatically, devil Kaz>devil Jin. Kazuya wins.
Mishima's aside, though, I think it was stated that Paul was the strongest male in tekken. He was even on par with Kazuya in tekken 1 days. Although that was then, and now feng has been here for several games now and has proved himself tougher than most of the other main cast. So either feng or Paul. If it came down to a fight to the death, feng.
NINA KAZUYA FENG
Tekken, Syphon Filter, Metal Gear, Splinter Cell, Street Fighter, Soul Calibur, Mortal Kombat - Favs! I have 3 PSNs: The_Buff_Guy, Liam-1, and I_Enjoy_Tekken
Strongest Male: Jin/Devil Jin - Arguably the strongest Mishima and currently undefeated, IIRC.
Strongest Female: Nina Williams - Consistently portrayed as a formidable foe, both in the games and the movies.
This is how I would rank the fighters based on their portrayals as of Tag 2.
(S) Mishima/Supernatural: Jin/Devil Jin , Kazuya, Heihachi, Lars, Jinpachi, Angel, Ancient Ogre/Ogre, Unknown
(A) Badass Normal - Not a Mishima/Supernatural but are almost capable of matching them: Nina, Zafina, Raven, Yoshimitsu, Bryan, Feng, Alisa (Safe Mode off), Jun
(B) Masterful - Very proficient with their fighting style, but not quite on the Badass Normal level: Steve, Bruce, Dragunov, Anna, King, Armor King, Marduk, Jaycee, Bob, Hwoarang, Baek, Bob, Kunimitsu, JACKS, Lei, Wang
(C) Street Fighter - Not much to say here. Just your average scrapper: Miguel, Leo, Lee/Violet, Eddy, Christie
(D) Joke - Their sole purpose in the story is to provide comic relief: Lili, Asuka, Xiaoyu, Miharu, Sebastian, Paul, the Laws, Kuma, Panda, Dr. B, Slim Bob, Tiger Jackson, Roger Jr., Alex, Mokujin, Alisa (Safe Mode on)
Did I miss anyone?
http://bfbc2.statsverse.com/stats/ps3/EmiliaTheSage/ Women shouldn't stay in the kitchen and make sandwiches. We should join the "Battlefield."