As you say, I suspect a petrol would be better suited to the miles you cover, although a diesel might work if you do the occasional motorway run to clear the DPF. A Honda CR-V would be an excellent choice as it's reliable and practical. Alternatively, take a look at the Suzuki Vitara. The 1.6 petrol engine is very robust and efficien and there'll be plenty of room for your spaniels. It rides well, too.