A point I haven't seen mentioned here: diesels will last a lot longer -- often twice the lifetime or more of a gas engine.
That might not seem to matter if you "flip" vehicles every few years, but because of that lifetime, even used diesels tend to have higher resale value -- sometimes MUCH higher! I've seen a Dodge 250 gas pickup for $500, but the Cummins diesel version in the same year will fetch $5,000, because the engine hasn't even hit half its life yet. Some diesels should go a million miles with only a couple expensive maintenance items, typically, rebuilding the injection pump every 300,000 or so.
(Of course, the brakes, electrical, and other running gear ages the same on a diesel as with gas.)
The fuel economy is often dramatically greater. A mid-80's diesel Jetta will get the same highway fuel economy as a new Prius! My 1991 Dodge Cummins gets 20 mpg, while the gas version gets 12. My diesel step-van gets 14, the gas step van I replaced got 7. If, as I do, you believe fuel costs are going to continue up and up and up, this may be a huge consideration.
Finally, if you think that biofuels are the future, consider that a diesel running on biodiesel will perform within 5% or so as well as it will on petro-diesel. But a gas vehicle running on ethanol will lose about 30% of its power and fuel economy.
I make my own biodiesel from restaurant waste oil -- it's relatively easy, compared to making ethanol.
I'm also of the opinion that maintenance is cheaper than that of gas engines. Diesels are MUCH simpler than spark-ignition engines: it either isn't getting fuel, or it isn't getting air. The heart of a diesel is the injection pump, and those are pricey to service or replace. So you tend to have low maintenance costs until you need a pump, then a big bill every few hundred thousand or so. But over the lifetime, I'd have to say diesels have lower maintenance costs.
But the real question here is, do you consider yourself mainstream, or a bit eccentric? If you like the "edge," and are trying new and different things out, go for the diesel. But if you cringe and being out of the middle of the bell-curve, gasoline is best for you.
I'm not interested in the inner workings of petrol vs. diesel engines, but more in what would be of relevance to an everyday buyer when choosing between diesel vs. petrolI'm not sure this is about motor vehicle repair. This seems more like a shopping question, which would be off-topic here.