If you live an area that's prone to earthquakes, has had frequent NG outages in the past, or doesn't have NG, then a diesel generator might make sense.
If you live an area with NG, that rarely has a NG outage, then it definitely makes sense to go with a NG generator. If you're still really worried about a potential gas outage, you could get a dual-fuel NG/Propane model.
A diesel generator will have 2-3x the acquisition cost, higher maintenance costs, far more expensive replacement parts, and be harder to find parts in an emergency. On the other hand, a Kohler residential LPG/NG generator uses a standard commercial V-Twin engine with cheap and readily available parts. You could drive down to any commercial power equipment place and find just about every part in stock.
Home heating oil has been the exact same ULSD fuel as on-road diesel for many years now. It's just dyed red. We've been renting a 200KW CAT Diesel generator for the past several months at work with a scheduled weekly fueling by the CAT dealer. They just send a home heating oil company to come and fill it.