Hmm, deceptively tricky topic this month. I'm gonna simplify things for myself and go with "best" as most popular on flickr and that comes in the form of this one:
Into the fire
Into The Fire by
Brettus - Brettnet.co.uk, on Flickr
Taken almost 4 years ago now by a friend and I heading to an abandoned WWII compound and trying various light painting tricks, this was one of the simplest but most striking. 10 second exposure of my friend Andy spinning steel wool which has been ignited with a battery, what made this one different was that the "sparks" were contained just within the mouth of the corridor with just enough flying off to keep it interesting and add movement to it.