Varus Question

So after doing some reading (And wondering why I lost the HUD notification on-hit when I coincidentally swapped to Thunderlord's) I found out that Deathfire Touch shows a ring around your character pointing to the enemy you hit. This is awesome for Varus as checking bushes couldn't be easier!

Then I started thinking.. how effective is Deathfire Touch anyways? Not gonna lie, I've killed a lot of people with Deathfire Touch after hitting them with my Q. It does alright damage, but how much really?

So I'm asking y'all if Varus' Q is considered an AOE or Single Target (Assuming it's AOE). Since the damage on DT scales with the type of spell cast, and the internet is full of everybody claiming different things, I figured I'd come here and ask :D

Also, what's the deal with everybody's ult overriding mine! When a Hec charges me, and I ult him midcharge, he should stop dead in his tracks ;( oh well.

-Xykaru