For gaming, either the 880 or 990 would be best as they are both open backed, so there is a better soundstage and for games like Counter-Strike this is essential for hearing footsteps and sounds behind/to the side of you. And better in all games in general, although I do hear of people who prefer the closed style for this as it makes things like explosions and gunfire more....."explosive" if that makes sense. My vote goes to either the 990 or 880 though, leaning towards the 990s as they have a more fun sound sig. For movies, this is a preference issue. 880s will sound a little more natural whereas 770s are a lot more bassy and congested, great for action movies etc but for natural sounds like speech the 880s or 990s will be better. But this is more of a preference issue, and in the grand scheme of things all 3 will perform admirably here. For music on the go, you'd probably be forced to go for the 770s as the 880s and 990s do not isolate you at all, neither from outside sound coming in or from your music escaping. Impedance depends on what you're going to be running them off. I'd try to get the lowest impedance you can, as there is little sound quality change among the various impedance models. For the PC, get a decent DAC and amp combo like an O2/ODAC combo or similar Fiio model. However for portable use the only model there that would be applicable would be the DT770, and for these I'd suggest getting the 32 ohm model in which case you can forego an amp completely, on PC or mobile.