I agree with the others here. Iron sights, No doubt about it.
I'm the type of person that'll simply leave guns plain as pie. Only exceptions are sniper rifles, but even then i'm working up iron sights for them. I just find them a lot more easier to aim with.
Depending what kind of iron sight it is. Iron sights don't block your feild of vision as some optics do, or distort it with the magnification of a scope. Sure, magnification is helpful, but thats why you just carry a small pair of binoculars or a monoscope with you to do the same job. No need to seek out targets through optics when you can simply line up your sights on them.
Only optics I use these days are whats on my sniper rifle and whats built into my G36. But that is soon to change.