I'm a lv 83 druid and my strangling vines was maxed out (20/20) and could damage up to about 180 each tick, my lighting strike was maxed out and could get up to about 380 and my storm touch was also maxed out and got up too 950 damage. Though storm touch did a lot of dmg, it took a long time to cool down and I could get about 2 lightning strikes in each time it cooled down so the overall dmg for lighting strike was about 650, but strangling vines was the most useful. Not only did strangling vines do a lot of damage over time, it also helped when I missed the enemy with lighting strike or storm touch because strangling vines never misses taking damage. The end result was strangling vines taking around 850 off the enemy so in conclusion I think strangling vines is better although all of the skills are sometimes more useful than each other one way or another.
Soz its so long but I hope it was useful
(This is all just my opinion, you may feel differently and I accept that)
