As many have said, it all depends on purpose of the rifle. All of my AR's are for short distances. On my SBR, I run a Trijicon MRO in a QR mount so I can move it from rifle to rifle. . On my 16" rifle I have a Vortex Strikefire II. I have a Vortex 3x Magnifier on a swing-out QR mount that sits in my rifle bag, so if I want the option, I have it for either platform.
If I could afford it, I'd buy an ACOG for my 16" rifle.
I've considered trying a Prism red dot 3x or 4x, but just chose to spend money on other things.
Way back when I had an EoTech 512 on my original Bushmaster (back when it was great - not a Remington AR), and to this day, I think that is probably still my favorite red dot sight for the AR platform. I will probably own one again some day.