I planned on using the BOT quick wraps in the trailer so I wanted as much leg coverage as I could get. I got a 14" set for his front legs and 16" set for the back. Works great.
Honestly, I don't believe there is much difference in the circumference in the BOT quick wraps. It's more about how high you need them vertically. I never measured, but I don't noticed a width difference between the 14" and 16' set I have. But of course, its quite obvious the 16" set is taller.