Hey buddy, not trying to be a wise a**, but just letting you know you're going to get alot of mixed opinions on this subject. Which is why I'm gonna save the hassle for you and just have you use Nico's Altima Coupe search engine. You may find you're answer there, but mainly it's going to be mixed opinions. It's kinda like that with intakes and exhausts as well
I can tell you whats currently popular and that is the Eibach springs. the give a 1'' drop (1.4'' front and 1'' back I believe). Some will go lower like the H&R springs.