Console players what response curve is most commonly used and what sensitivity do you guys play at?
Classic is the most common. Some folks play linear but it's rare. Some players also use the ALC settings, but again less common than classic.
People tend to play between 4 and 6 sensitivity for regular camera control, and 3 and 5 for ADS setting. I'd say the most common is 4:4 or 5:4 among good players.
3:3 is probably the most common setting among all players, but only because it's the default. Personally I play 4:3, I prefer the lower ads sensitivity.
This is me using 4:3
I think the most important thing for developing good aim though is really just
a) picking something sensible that you can reliably control. So, 8 ads sensitivity is probably too hard to control accurately, physically. Like no matter how much time you put into that, most people are going to be making compromises to their accuracy if they go too high. With that in mind, staying within that range I mentioned above is probably a safe bet, although of course people can experiment to find what works best for them.
b) grinding it out. Accuracy comes down to learning your controls so that they're absolutely intuitive. It can take weeks to get good on a certain sensitivity but honestly, you're constantly finding yourself getting better so long as you stick with the same settings. That isn't to say that you should never change though, but changes come at a cost and regularly changing your sensitivity is likely to hurt you a lot (I know this from experience).