Maybe it does determine preferred race?
My favorites in order-
Spitfire
Starlight Glimmer
Fluttershy
Twilight
Rainbow Dash
My favorite type of pony is pegasus, followed by unicorn. Three of my favorite characters are pegasi, one is a unicorn, and one is an alicorn. I don't think my favorite characters determine preferred race, and maybe abilities and stuff determine preferred race.