The VW is a top van, in particular the new ones.
The dispatch is a good van, but a 650l tank is really right up there at the max load limit.
I know one guy who has a full 1000l IBC tank in his Dispatch
He copes fine, but he is at risk of a hefty fine if he is pulled over and weighed.
The new VW drives like a car too.
My own van is the nissan Primastar, not a cheap van to be sure, but highly rated and cheaper than many to insure due to high security levels in them.
If you can afford the VW then I would go for that one, it's greater load carrying capacity would swing it for me.
If you want to use something like a full 1000l tank then something along the lines of the Relay/Ducato would be a better bet, on an earliar thread about vans the price of the Ducato was very good indeed...or at least the price you could get one for.
I know there is a third van that is also the same as the Citroen and the Fiat, but I can't remember it
I went round and round in circles for months before I eventually settled for the Primastar.
It drives you potty
Ian