Best op DoT is root even though many regard it as useless. Doing some tests today. My flames of insanity dealt 23 3 times which is 69(lol) damage. My root did 44 2 times which is 88 damage and my anguish did 53 once unless you count the initial hit. Now anguish worked like 2 out of 5 times.
Another factor you can perma root since it lasts 6 seconds and its cd is 6. Flames of insanity deals its dot faster but cd is higher and the stun chance isnt 100%. Root is essential for a team op. For the hard hitting vulars perma root is insanely useful. Hope you ops invest a point in root because it makes you insanely valuable.