Sun Country's fleet is avg 3 year old Next Generation 737-800. All seats are leather. Overall, FC has 39" pitch and 21" width and Y has 31"-33" pitch and 17" width. Not sure about Exit Rows. Seats are comfortable - better lumbar support and more padding than NW's.
Note: NW's FC pitch is 36-37" and coach is 30-32".
Sun Country has Audio Entertainment at each seat throughout the plane and serves a free hot meal in FC and Y.