You will find many pros and cons when people are discussing ballheads. I started out with this one before I had any lenses heavy enought to justify the purchase of a better quality gimbal head. If you are mounting a lens that weights more than 5 pounds, save yourself a hassle and purchase a gimbal head instead. Ballheads are 'toys' by comparison and even the best ones offer far less versatility when tracking a moving subject. And the prices of the top quality Kirk or RSS ballheads rival the cost of a Wimberley gimbal head anyway, so you may as well just get the right equipment the first time.
Bogen offers ball heads with several different configurations of quick release plates, but I chose the RC0 shown above because the hexagonal shape is larger and sturdier than the other ones offered. When I purchased it, I was mounting the Canon 300mm f2.8L lens and Mark II N body to it, which weighs a total of over 10 pounds. This ballhead was able to hold it, but I found that if I didn't tighten it down securely, the entire rig could drift to the side and eventually slip. For this reason, I purchased a Wimberly W200 gimbal head to use instead, when working with a heavy lens/camera combination. The design of the gimbal head makes it impossible for the rig to fall at the point where the camera is connected, so it's as much insurance as it is for ease of use. I rarely use the ballhead anymore, and only for lighter duty work. It stays mounted on my backup tripod. The Wimberey head can be seen here: http://www.pbase.com/tim32225/image/89954237.