I have had good and bad experiences with muffler shops.  Don't be afraid to
go non-OEM, as long as you talk to the guy who is doing the work.  Get under
the car and point out the intricacies of the mysterious Volkswagen.  Show
them the importance of the hangers and mounts.  Tell them to overlap the
pipes by 2" and then weld them (a butt weld won't last!).  Your best bet, in
my opinion/experience, is to find a small privately owned shop and chat up
the owner.  For $50 I got a muffler, a lifetime guarantee, and a new muffler
strap.  The new muffler had larger diameter pipes, too.  (reduced back
pressure).  Just remember, talk to the mechanic! (and don't let him weld a
hanger to the body)

Good luck

Bill Marshall
85 Vanagon GL/Tiico
PHX AZ