There are currently 3 different PS4 Models; the original PS4, the PS4 Slim and the PS4 Pro.
The original PS4 is currently being phased out, replaced by the PS4 Slim, which has the same specs but is a third smaller. Both are available as 500GB and 1TB, and like the PS4, come with HDR due to a recent PlayStation update.
The PS4 Pro is the most powerful PlayStation ever, allowing you to play games in 4K. It is currently only available in 1TB.