I just got a medium Carly in saddle today so I definately say SADDLE. Also, the medium certainly is NOT 15" across, it's like 10.5. ;P Still fits my needs tho!
The large measures 15 inches across in real life - not 17. And it's about 13 inches high and 5 inches deep. It is a big bag - but I love her. Just for reference though to put the pic into perspective I am 5'6" and 114 lbs. So the bag probably swallows me up a bit - but I don't care!