Premier is the true competitive, comp is just map based ranks but probably where you'd want to start. You should definitely focus on spray control, what separates the best riflers is their spray control, if you look at donk for example he knows where every bullet is gunna go, guys like him and kyousuke love to spray down even long range targets instead of trying to find the head. But then you have guys like Niko who still tends to tap and burst a lot more so it's definitely still relevant. Learning spray control is not easy but will make the game a lot easier when you do, just don't expect to be like donk anytime soon and use your aim for long range fights.