Energy's knockback is nice to stop mobs hitting you as much, elec has -end on the mobs and gives you a nice end recovery power. Energy's knockback goes well with storm's knockback.
At the end of the day, just go for what will give you most fun. I've taken energy, havent looked back 
Yep, I've seen both and as above both ahve pro's on there. I would go by what you feel best playing.
Energy's Knock Back will go well with storm and good damage output from it too.
Elec has good dam as well, no KB but -end to opponenets. Although simply using that won't make a massive dent to your enemies. Elec does ahve a hold which would stack well with thunderclap in PvE and for isolating bosses.
hop you make the fun choice though m8ty 
Just whondering over the pro's and con's over storm/elec and storm/energy.