Favorite: Existentialistic
It sounds awesome, and uses an X which is awesome, just say it out loud, it rolls off the tongue and lingers in the air pleasuring the eardrums of all involved.
Least Favorite: Ignorant
This isn't so much the word itself, it's the people that use it, hearing it used incorrectly or as a general insult for someone who doesn't believe the same thing you do has ruined it for me, also the hard IG sound makes my skin crawl.