Ahh, glad "phantasmagoria" was mentioned. That's generally what I give as my favorite word.
Purely on sound, I'm a huge fan of "clusterfuck" and "electric". "Fuck" really is such a versatile little word xD
For a combination of aesthetic and definition-related reasons, here are a few favorites:
"ethereal" - relating to the otherworldly, or lacking material substance
"harbinger" - something that foreshadows a future event
"capricious" - fickle, given to sudden changes in mood and desires
"synchronicity" - the simultaneous occurrence of events that seem related but have no causal connection.
"vehement" - strong, zealous, impassioned