It's kinda situational for me. If I'm playing a cocky/arrogant jerk I'll bring out all the guns in my arsenal, which includes the 3 taunts, dash dancing, and tea bagging throughout the match.
If it's a close match I like to use his up taunt - I feel the pose Luky strikes, the rush of Aura about him, and his shout are a sort of "I overcame" type of adrenaline rush and it feels the most powerful of his taunts. I like to do this one in Sudden Deaths. Sometimes I'll also dash dance if the opponent is in the screen or star KO animation
If my opponent rage quits or I'm feeling bold and am sure I'll win the match I'll do his side taunt. I'm not really sure why but I like using this one in this type of scenario the most; no real reason =P
If I land a flashy KO I like doing his down taunt. The pose he strikes looks like a real "come at me" type of taunt and I feel it looks best and is most effective after doing a disrespect or flashy kill.
Sometimes I'll also Extreme Speed off the top of the screen if I have enough Aura. I don't do this one a lot, but I'll also crawl sometimes - forwards or backwards in the direction my opponent died in =P
