The primary difference between the two models is their passenger- and cargo-carrying capacity. If you need to carry more people, then the kombi model is probably best for you as it seats a total of five or six (including the driver). However, the extra seating does compromise the available cargo space. If you need to carry more cargo, then the panel van will be your best option. It offers seating for the driver and up to two passengers and has significantly more space in the back.
You can claim back the VAT on either version: panel van or kombi.