What's the difference between the Red Dot and Reflex sights in Call of Duty: Black Ops?
Taken from COD Wikia:
The differences between the Reflex Sight and the Red Dot Sight is the Reflex Sight has a slightly larger field of view when looking through the optics.
Personally, I am a bit more comfortable with the reflex sight than with the RDS.
Tactically, there is almost no difference.