Deathfire Vlad is Best Vlad

If you peg your opponent on-cooldown with Q, you will far exceed the damage of Thunderlord's when using Deathfire Touch. For example, lets compare a level 9 vlad with 120 AP:

Every 20 Seconds: 90 + 12 = 102 damage from thunderlords x1 Every 20 Seconds: (8 + 24) * 5 = 160 damage from deathfire x5

That's 60% more damage. You really just need 3 procs to roughly break even. 4 will do more damage, and 5 will dominate. Late game, the damage done over 20 seconds becomes greater as AP increases. For example, at level 18 with 400 AP, deathfire will do double the damage of thunderlords over 20 seconds. That means for any fight longer than 10 seconds, as long as you can keep applying deathfire, you will do more damage than thunderlord's.