I will begin a thorough study of the OpenBSD and FreeBSD, which are the most complete books?
I found these, which are the best?
Check out The Complete FreeBSD by Grey Lehey, available for free. Greg is a good guy and used to be part of the FreeBSD core development team. Maybe he still is, I'm not sure. The book is probably a bit out of date, it seems was last updated in 2006, but it would be a start at least.