I've seen them all and six is definitely the best of the lot. Not that the first five weren't good but they skipped all around from subject to subject in each one and there really wasn't that much information in them that we haven't already seen here on the forum. Number six was much better since it focuses on just one dedicated subject in depth. It is filmed in Peru and like I said, "best of the lot"! The first five should have been what number six was.
You can watch the first 4 on Amazon on the cheap ($1.99 each), by the way.
http://www.amazon.com/The-Watchers/dp/B0085F78I4/ref=pd_cbs_mov_aiv_3
http://www.amazon.com/Watchers-2/dp/B007K0GCKK/ref=pd_cbs_mov_1
http://www.amazon.com/Watchers-3/dp/B007K19V16/ref=pd_cbs_mov_aiv_1
http://www.amazon.com/Watchers-4/dp/B008X0TMRG/ref=pd_cbs_mov_aiv_2
!! FOXTROT JULIET BRAVO !!