Both florescent nylon and firefly front sight inserts have their place.  Which is the best and for what applications?  It depends on who you ask.  For me, this is what I do:

Competition:  I am torn between the two choices.  I believe the firefly insert is very fast at close range, though it takes me a smidgen longer to make the pyramid for longer shots.  I don't know if it's the same for everyone, though that's the way it is for me.  

Defense:  Obviously, in darkened environments, my pieces are sporting fireflies.  A case in point was tonight:  I walked the trash can up the hill about 60 yards from the house on a dark night with only a sliver of a moon to help.  Of late, we've had cougar, bear and bobcat  sightings in our neighborhood.  So, I gave my Sig Sauer P225 9mm (I know it's little light for the bigger beasts, but that's what I had with me) a dash of florescent light from a mini-uv flashlight I had just purchased.  Just two seconds of mini uv key chain light and it stayed bright through the walk and for sometime later.  I have to admit that the former night sight hater me felt a little more secure at the notion that I could throw a big bright glow on any shadow, in just an instant.

Hiking and hunting when camping is not involved:  In these situations, I don't plan to be out overnight and I often have a pistol topped with a standard florescent nylon insert.  I do so because the day colors are brilliant and the after sunset view, in case I'm out later than I wanted to be, is very bright.  The uv filled sky lights up the florescent nylon inserts, as if they had a lamp under them, after the sun has happened and as long as the shadows remain in the grey zone.  Of course this is a boon for hunters, as most states limit hunting to 1/2 hour before sunrise and 1/2 hour after sunset.  In that lighting, the florescent nylon inserts stand out well on dark animal hide. 

About that mini uv key chain flashlight:  I really like it.  It's small, bright enough to do the job and inconspicuous on my key chain.  Don't be surprised if you find it on our website store at a price that can't be ignored and/or accompanying certain promotions.