Personally, I would go with the gasoline powered Excursion if you have no strong opinion. The diesel powered ones are very nice, but truly for a daily driver that likely will not do much towing the V10 is sufficient. I have seen these modular V10 engines in this application go well over 200,000 miles with little to no maintenence issues, which for most of us would be our ownership life of the vehicle. They have good power, just not a lot of torque for heavy towing. The mileage is not great but not horrible and well in line with other vehicles of similar size and weight. The 7.3L diesel is a good option also and can be modified if one desires more power, for not a great deal of money. The 6.0L jury is still out. Many who bought them, especially later in the run, found them to be good engines with good power, but they really do or did not get that much better mileage unladen than the V10. There are still enough lemons floating around out there among the 6.0L that I would find it hard as a potential purchaser to tell easily so it might be best to avoid that engine unless one knew the seller personally or had solid records of any issues. The only thing I do not like about the Excursions is they tend to be rattletraps with age. The sheer size and voluminous cabin tends toward creaks and grunts from inside. While some might expect this in such a large vehicle I would find that annoying. As a large cargo hauler, they are pretty simple and bulletproof.
John M