Depends on what you want the head to be best for. I have an older, now discontinued Gitzo magnesium ballhead in their "classic center ball design",and is has three small,round locking knobs...I loathe it. It's lightweight, well-made, silky smooth, and--the three locking knobs are a PITA. One for rotational axis...a second for tension...a third to lock the head. Just wayyyy too many instances of confusion, and loosening the wrong knob. When the camera is tilted , or the head is turned, the position of the controls shifts.
I had an old Bogen Heavy Duty Ball Head, the 3055 I believe was the catalog number, for 20 years or so...I actually preferred it to any other ballhead I've ever used.
http://www.keh.com/camera/Tripods-Tripod-Heads/1/sku-TR429990044690?r=FE Why? TWO controls...one for rotation, the lower level, and ONE CONTROL for locking, the upper lever. Unlike with the older Gitzo, with the Manfrotto, "upper" and "lower" always,always,always stay consistent.
With the Gitzo, its three identically-sized, identically colored, identically designed, identical-in-fit-finish-and-feel control knobs mean that tension and lock are ALWAYS at risk of being confused when making an adjustment while looking through the camera. And of course, the rotation knob lock is also identical. I see that the NEW Gitzos in that series have done away with that type of messed up system.
I think for portraiture and things like that, the FEWER controls to run the ballhead, the better it works. ANd so, I would look for a minimalist, lever-tytpe locking system, at least for people picture work. I'd probably look for an entirely different type of head for studio work or landscape work. SO, as with tripods, the choice of head depends on the area you want it to be best at.