I just placed an order for the Knight's SR-15E3 IWS MOD 1 for $1800 with shipping

I can't be happier with this rifle and can't wait to put my hands on it. I will post more actual pictures of it when I receive it from the FFL dealer in Rochester.
What should I get for the optic? I only shoot mid to close range for now so I think about a red dot sight or holographic. Can someone give me an advice of what to get?
Thank you