Have 2013 and think the 2018 interior looks a lot better. Towing will probably remain the same since power train is identical to the 16 and 17 model year.
The S550 is the first Mustang I was interested in and bought since my wife bought a new 1973 Mustang Grande. I did test drive a new 1968 GT but wanted a larger vehicle and settle on a 69 Torino fastback. To me, the S550 is the best looking Mustang in 50 yrs.