Carousel at 6 flags

I went to six flags a couple of days ago and was trying to get my daughters to make an informed decision about which horse to choose.

The kid running the machine says, "the horses go 3 miles per hour" and I thought -- it's impossible that they all go the same speed. So, I decided to take a few measurements. This is what I got:
time for 1 revolution: 28.5 seconds.
outermost radius: approximately 33 ft
innermost radius: approximately 20 ft

So, was he right? Also, which horse is the better one to choose? Why?