Regardless lightning can set up pretty amazing single target burst and decent aoe pressure/burst thanks to chain lightning. The capability of the spec varies based on the amount of the enemies around and the capability of your teammates to peel/guard you if need be. Full lightning is by no means 1v1 spec and you should avoid such confrontations; you need a group setting to maximize the occurrence and effectiveness of your procs.
That's a big if, and basically admitting you need help to do your job. Chances are if you're in that good a team that you're able to freecast most of the time, it wouldn't really matter which spec you use.