Frankly, you'll either never find such or it will be too expensive. Remember you did ask for "best."
The rest of us may just enable AUDITING that is in Windows NT 4.0, 2000, XP and beyond. Since I can just audit so much with this supplied feature, I have no reason to do much else.
The same auditing can be turned on in Linux. I have no experience what you can do on your Macintosh.
A book on such -> http://www.amazon.com/exec/obidos/tg/detail/-/157231818X/104-5602560-7683961?v=glance
I am looking for computer monitoring software, that can monitor what occurs when someone uses a computer.