This might be a long post.  I have been working at bike shops for about five
years selling bicycle transport systems so I've given this speech hundreds
of times.

I have carried up to twenty bikes on my vanagon.  Here are my thoughts.

1. Roof rack is great for strength, not good for mileage or ease of loading
and unloading.  You can also carry some other things like boats or couches
or rooftop boxes.  They make your vanagon look tougher and ready for
action.  Here is mine fully loaded with eleven bikes when I was moving to
the Pacific Northwest from San Diego.

http://www.flickr.com/photos/kerryandlee/288695822/in/set-72157594360476596/

2. Trailers are also very useful for things other than bikes.  I bought a
trailer from Harbor Freight for the above move and loaded it with a few
hundred pounds of stuff.  You can see it in the pic linked above.  As
mentioned in a earlier post it did bounce around a bunch when it's empty or
mostly empty.  Also it must be registered and have a plate on it.  You must
also wire your vanagon for trailer lighting.  Small trailers are very hard
to back up.  I can't see mine in my mirrors untill it's practically
jacknifed.

3. Hatch rack's are good for up to four bikes and can be removed and
installed on another vehicle if the need be.  I have one on my van in the
above picture as well.  Try and get one from a good brand like Thule or
Yakima, the wallmart ones will break or damage your vehicle, I had one give
out on me after only a few uses when I was living in Colorado.  I'm sure
having three heavy bikes on it and going over a few high mountain passes in
my syncro led to it's early failure but, that's what we do with these vans.
Doesn't affect mileage or crosswind steering as much as a roof rack or
trailer.  Hitch racks are usually the most affordable option but the least
able to carry cargo other than bicycles.

4.  Hitch racks are my favorite.  They require a strong hitch be installed
on the back of the vanagon but it's a nice thing to have anyway, it's good
to be able to tow small things and makes a good winching out anchor point
when you get stuck in baja.  I have no doubt about the strength of my Dennis
Haynes hitch for this.  A hitch that bolts on the tow loops may not be the
best idea.  I have a Thule T2 and love it.  I only have the 2 bike rack but
may upgrade to carry 2 more if I need to.  There are many other
manufacturers that make quality hitch racks, Yakima, Sportworks, Saris all
have great ones.  My favorite ones use the wheels to attach the bikes to the
rack.  This style will take almost any kind of bike, some of the hanging
style racks are difficult to use with smaller frames or step through style
bikes.  If you ride mountian bikes and get muddy the hitch rack keeps you
the cleanest when loading and unloading the bikes.  If the city buses in
your area have bike racks in the front they work just like those.  The
quickest loading and unloading of all the options.  Can be moved to any
other vehicle with a hitch the same size as yours.  It is an expensive
option but not much different than the trailer if you factor in the wiring
and registration fees.  Doesn't affect mileage or crosswind steering as much
as a roof rack or trailer.  I can see the bikes in my rearview mirror while
I'm driving.  Bikes are loaded and uloaded the quickly and are lockable.

Here is what mine looks like

http://itsthewater.blogspot.com/2007/03/my-thule-t2.html

I hope this helps you out, Clint.

Lee
89 Syncro