Help me please, /k/. I'm trying to decide on a decent sight for my AR, and I've decided I'm going to go with a Primary Arms brand. They're not too expensive, have great reviews, and I don't plan on fighting any wars with it so it should be fine. But I need to decide between the two images that I'll post below. First is the Red Dot sight, second is a 5x magnification optic with a reticle that is very similar to an ACOG.

My issue is that my AR is small and more suited toward a red dot, but I have no experience with them. I have a lot of experience shooting with ACOGs but they're too expensive. Also, my AR has a 14.5" barrel (with pinned comp) so I'm not sure if the 5x optic will be as useful? Is it that much different from a 16" barrel? Should I just get the red dot and try to learn how to use it?

Pic related is my AR. I'll be filling this thread with girls with guns while I wait for replies. Any help or advice is appreciated.