Fire is safer. You can always block-cancel, E-cancel, Q-cancel, etc. out of flickers and pierce. It's not bad for learning boss patterns, doing Mushin's Tower, or tanking in one position with the boss facing one direction only.
Lightning does more DPS against the punching bags NCsoft calls dungeon bosses. Make sure to spec flicker straight down for that 5% crit buff, sundering for chi, and ss for extra draw stance.