Swivels come in a few different types. The National Admiral and Admiral CT have a standard swivel that turns 180 degrees into the cab (driver or passenger). The Knoedler Chief line of seats as a pneumatic (air assisted at the touch of a button) swivel that turns 180 degrees in either direction. That is nice if you tend to swap your seats over to the passenger side when it is time to replace you truck seat. Bostrom Wide Ride II has swivel as an option. Just beware that swivels can add 1-2" to your seat height on most seats. The Knoedler sits lower than average but the Admiral and Bostrom Wide Ride sit fairly high already. You may want to look at the Bostrom Wide Ride II with a low profile base, if you are consiering swivel.
All prices are in USD.