Might try a higher emphasis on Q just to see if that's valid.
And far as picks go-
I've noticed I have a higher success rate with Caitlyn, Varus, Draven, and Tristana. So either high range ADCs, or ranged ADCs with very powerful poke / potential burst damage tend to do well with this, again of what I've seen; I'll need to do a lot more games before I have a guarantee on that. Not done well with any Ezreal ever, though that might be for .. other reasons.
Enemy wise.. Blitzcrank was surprisingly not much of a threat. Proper warding / positioning means you can basically assume where his Rocket Grab origin will be, and since he's locked into the animation for a moment, you're very likely going to stun him + a well meaning enemy ADC. Tends to bait them if anything.
For that matter, sustain supports I've done very strongly against. Sona/Soraka have been very easy to deal with. Taric faired better than the above but was surprisingly easy to deal with; long animation on Dazzle, near melee range on W + R, and some Taric's desire to get in an occasional auto for his passive really hurt him in that match up. He can't zone your ADC or be aggressive at all like he normally could.
Leona however, has been quite troublesome every time I've gone against her. MIGHT'VE BEEN THE PULSEFIRE EZ I was supporting both times, but I'm thinking she's possibly a strong counter.
Enemy ADC... Graves has been really easy, his Dash typically gets him stunned right on the edge of Well due to how it works. Ezreal was no real issue, he won't get caught much but it's easy to zone him or bait him into bad engages. Didn't have too much trouble with Ashe, and really, any ADC who stops to poke with a skill tends to be easy picking for me in solo queue at least.
Jungler wise, pretty much as simple as this. Most melee junglers, due to my Exhaust, Well, Ult, are hilariously easy to diffuse, even the ones that have large gap closers (I just have to not get baited into Welling at a distance, like with a Xin Zhao jungle, since he'll dash out of Well to my ADC before it stuns). But, there are exceptions. Olaf does not care about Support Viktor, at all. lol
Caster type junglers are hit or miss. Doesn't seem too effective at stopping an Amumu jungle, period. I have to hope I'm reaaaaally responsive with that R.
Far as working with junglers goes, Amumu's a godly pick. There's no point in the game Amumu Ult > Gravity Well > Viktor Ult (or different order as situation calls) isn't powerful as all hell, and it's kind of mindless to execute so I don't really need to worry about much coordination with a random. So he's kind of my favorite jungler to see in game. Strong red buff applicants / chasers are also great, since if I can catch an enemy with Gravity Well once, they're probably done like dinner. (And even if I can't, sometimes cutting off an escape route'll make them blow a Flash waaaaay early and that'll cost them their life.)
In an ideal world, I'd like to see comps with lots of AoE + disables. Amumu jungle Naut or Nunu jungle, Katarina mid, and if we have a strong AD presence jungle, a tanky AP top like Rumble, Swain, etc. The more Hit R to Win moments, the more results I tend to see against the incompetence of solo queue.