So much mis-information in this thread.
Technically the only Mishima's are;
Kazuya
Heihachi
Devil Jin
Angel
Categorized by the electric wind god fist. F,N, D, DF + 2 (to the frame and +5 on block with pushback)
Kazuya has a shortcut due to mist step which enables the notation F,N, DF+2 and a full launch with a 13f EWGF from first frame of recovery from the abolishing fist punch. (Df+2) if you have the skills (very few do)
If the character doesn't have this EWGF move they are not Mishima fighting style period, regardless of storyline affiliation.
Standard Jin does not fight in the mishima style. it's his own brand of traditional karate and his verison of the Electric hit's away and is actually called something different.
Jun and Asuka are Kazama style fighting art's. Completely different.
Jinpachi could be considered but his gameplay doesn't really fit with the true Mishima's
Laz is a mishima in blood only. His fighting style has nothing in common with them I believe it's the "tekken force" Marshall art's style.
Some people jokingly refer to Steve being one as well due to him being a creation of the mishima zaibatsu when Nina williams was in stasis and having lighting hit effect's and that haircut.....
As for the Best. My avatar probably gives it away but...
Kazuya easily. He was the original KOIF winner and is easily the most badass looking and unique. His storyline in the first few games was pretty in depth but now he has pretty much become a pretty base villain unfortunately.
Also imo the most fun and one of the series most difficult character's to master
I personally hate how they tried to replace him with jin in tekken 3. He was the original poster character of the game. I'm hoping for a reboot of the franchise going back to it's storyline root's for the next numbered version of the game
Btw however Heihaci is easily the most evil.. dirty old git.