I've seen most of those beauties, and they all are BRUTAL!
Following is how I judge how hard/brutal any ballbusting lady is:
1. She's kicking him as hard as she possibly can without holding back anything, and the sheer physics show it. The top part of her body is bending backwards, and her arms are up and back to add additional body momentum. Her entire body from her head to her foot is involved in one orchestrated movement with all the energy ending up where her foot impacts his balls.
2. There is a very audible, loud slap/thud upon impact and you can see his whole body physically respond followed by a loud yell and his dropping to the floor. And unless he's naked, you don't get the full evidence of impact. Seeing and hearing his penis and balls slap into his abdomen adds to it.
3. The most brutal girls all seem to convey a sense that they have a deep rooted anger or hatred to men (or that man) and it is both cathartic and enjoyable thing for them to kick men in their balls (I've read some of their blogs on this). I've posted on the femaledom.com blog about this and how one of Sharon's girls seemed to go after one guy particularly harder than she did the other men. Sharon confirmed this and said that that girl had a personal dislike of that particularly man off screen due to his trying to date her. I think Sharon may have intentionally then started to put the two together even more such that the girl could enjoy kicking him in his balls as hard as she possibly could while Sharon filmed it. If so, it was a wonderfully brilliant idea of Sharon and was great to watch! :D
4. Lastly, permanent damage of the man's balls is not her fear, but instead her goal.
As it pertains to Femaledom.com, the following are probably my 10 favorite in terms of hardest kicks, although out of over 100 to chose from, it's a hard choice (Sharon, who runs the site, knows I'm an avid fan and post select photos of her to promote the site):
1. Amy
http://img17.imagevenue.com/loc949/t..._123_949lo.jpg
2. Andrea
http://img109.imagevenue.com/loc1141...123_1141lo.jpg
3. Cara
http://img223.imagevenue.com/loc586/..._123_586lo.jpg
4. Denise
http://img221.imagevenue.com/loc459/..._123_459lo.jpg
http://img136.imagevenue.com/loc110/..._123_110lo.jpg
5. Jill
http://img220.imagevenue.com/loc374/..._123_374lo.jpg
http://img243.imagevenue.com/loc191/..._123_191lo.jpg
6. Randi
http://img139.imagevenue.com/loc899/..._123_899lo.jpg
7. Lara
http://img194.imagevenue.com/loc14/t...3_123_14lo.jpg
8. Amanda
http://img166.imagevenue.com/loc437/..._123_437lo.jpg
9. Katja
http://img106.imagevenue.com/loc182/..._123_182lo.jpg
http://img102.imagevenue.com/loc500/..._123_500lo.jpg
10. Elaine
http://img240.imagevenue.com/loc75/t...5_123_75lo.jpg