I have a big head. Shockingly, the S Rudy Project Kontact+ fits me great. The L size, in spite of allegedly being the "right" size for my noggin (59cm, right in the middle of the range given), was like a friggin' salad bowl. If you're a 60 or under, the smaller size of the Kontact+ is a good bet. Stay away from the large unless you look like this guy: