Chris,
Get both of them.  After you buy the Bentley, the additional cost of a Haynes
seems like a trifling amount.  Be forewarned: neither is without errors and
inaccuracies.  Since I am accustomed to exact "as-built" documentation, the
errors I have found in the Bentley wiring diagrams are particularly irksome.
This is not solely a problem with the Bentley Vanagon manual but also their
other titles I own.  At least with the other marques, manuals are available
directly from the manufacturer.
Rich