The six PS3 Eyes configuration is the most accurate but it's also a more difficult setup and use--if you can manage the practical requirements (space, clothing, lighting, etc.,) and hardware specifications, and you don't mind the extra work, it's recommended.
Dual Kinect is a little less accurate but much easier to use. This is my preferred configuration because I don't have a lot of space to work in and I like the convenience of getting the work done much more quickly.
That said, I also have six PS3 Eyes
just in case I need to capture something that the Dual Kinect system is incapable of. To be honest though, I haven't had a need to set up the six PS3 Eye system for a few years now--Dual Kinect has worked out fine for the various projects/productions I've used it on (our shorts 'Happy Box' and 'Don't Fear The Pooper' (still in production), and for vfx shots in a couple of feature films.) The one downside to Kinect is that you have a smaller capture space than with PS3 Eye, but I've usually been able to work around the limitations of small space captures by merging multiple mocap sequences in Motion Builder. I believe you can do similar mocap mixing by using online web services like
Ikinema Webanimate. I haven't tried Ikinema myself yet but because my version of Motion Builder is getting pretty old, I've been looking around for a capable and less costly alternative for our studio.
Triple Kinect is supposed to be just as accurate as six PS3 Eyes with the benefit of easy set up and use. I've dabbled with it but only as far as seeing it work. I haven't use it in actual production yet but will do so very soon. (As usual, I'm up to my eyeballs in other work at the moment.) :p
I'm a little hesitant to spend a lot of money right now because a new version of iPi Mocap Studio may be coming out in a few months which will support the new Kinect and possibly other advanced devices. I'm really looking forward to this upgrade! :D
But if you need mocap right now, in my opinion, the current iPi Mocap Studio with a Dual Kinect setup is an excellent balance between cost, performance and ease of use.
G.