Diesel seven seater for towing

We are looking for a replacement vehicle for our Mazda6 wagon, with our 14-year-old son starting to hit his growth spurt and the recent purchase of a Jayco pop-top caravan. We're in north Queensland and most of our driving is long highway kilometres. I am thinking something diesel for the towing ability and economy, preferably seven seats, and have been looking at the Hyundai Santa Fe and the Isuzu MU-X. I have discounted the Holden Captiva7 for poor reviews, the Toyota Prado as overpriced and Mitsubishi Pajero as too old.