For daytime use, three choices:

A scope with the power range suitable for an AR15 Sport. Probably something like a 1-4x, 2-7x or a 3-9x. I'm using the latter on a dedicated hunting rifle. Leupold makes a Mark AR series of scopes with the elevation turret marked for standard distances for 55 grainers. (Mine is specifically the 3-9x Mark AR.)

A red dot that will crank up the intensity for bright noon conditions without "blooming", that is, putting a fuzzy halo around the red dot. I refer an Eotech myself, as it is useful for daylight and low light conditions, and is parallax free (which many red dot sights are not).

Williams makes what they call an AR15 Firesight. It is a sight base that attaches vertically to the front of a regular AR15. It holds an exposed green fiberoptic rod that bends over the top, presenting a bright green dot to the shooter.