Tekken fan here. It was the 1st game I ever owned for Playstaton. (Tekken 3 to be precise). What I loved a lot besides the quick action, are the great cut-scenes at the end of each arcade for the characters. They put a lot to make it look almost real in there. My favorite Tekken is 5 so far. Mostly because some of the characters I liked, where finally back.
My favorite male characters are Kazuya and Jin. But they changed Jin's moves for Tekken 4 and after. Good thing that Tekken 5 had Devil Jin, who had Jin's moves from Tekken 3/Tekken Tag Tournament and of course some new ones. So you could say that my favorite characters are Kazuya and Devil Jin now.
My favorite female characters are Nina and (was) Jun. But they killed her"-_- But, the good thing is that they brought back her moves in a cuter appearance under the name Asuka. I was so happy when I saw that she knew most of Jun's moves while having a nice appearance.
I have no clue about Tekken 6. I had originally heard that it was scheduled to go on sale this year. But if I'm not mistaken they postponed it for next year. We shall see^_^