the dmg is basicly the same but lightning seems to work better against heavy armored targets in pve, also it seems to increase the staggering when hitting someone and I think there are more items for fire resistance (like popular bk shield, flesh sweat).
Also its easier to reach the BS in anor londo.
I have **** of green shards and some red chunks and id like to do a flame weapon but i dont want to miss out on the lightning goodies.
So what has fire speaking for it?