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Well, this is a debate we've had in Europe, UK and now getting towards it in the US - for the everyday passenger vehicle.
Diesel cars are more expensive to buy.
Diesel cars are heavier, so all engine and fuel economy considerations aside, they will be more expensive to run over their lifetime because they will wear out all their mechanical parts (from clutch to wheelnut) more quickly than petrol cars.
Diesel engines with turbos are (generally) more complex than the equivalent 'total performance' petrol engine - which means your servicing costs are higher.
However.
Diesels are more fuel effificient, because of the way they work.
Actually, in absoulte lab-going-by-the-numbers terms, it's less cut and dried. Petrol engines have lousy efficiency under part-throttle - it was pointed out recently that if the government wanted us to be 'green' about our vehicle use, then if we had a petrol engined vehicle, to eek out maximum efficiency, we must drive everywhere at maximum attack.
Diesels have good efficiency under part throttle because of the way their combustion process works.
Both engines' efficiencies are improved by turbo-charging... but there are downsides. Anyone who has suffered turbo lag... or more commonly - stalled a turbo-diesel, will know what I'm talking about.
This debate, certainly within our circles, is exactly as
Famine says - it's based on what we want, not rationality. If we all did the sensible thing, we'd all go everywhere on electric trams and trains, and cycle to our local pick-up point. To replace all those 9 million bicycles in Beijing with crappy knock-offs is a monumental step backwards, but people are sheep, no matter where they live.
Any road-going 4-passenger vehicle with more than about 70hp is excessive... unless you live in Germany where one might say the 'agreed sensible limit' for their autobahns in 155mph, so maybe 200hp is about right. Anything more is not required, because it would be a luxury. Now you could argue that the speed limits should change to suit the revised high levels of safety in modern vehicles.
This is, of course, bull.
The amount of energy present in the human body travelling as a projectile will, by the laws of physics, increase as the square of the velocity it travels at. So when your 200mph Enzo hits a 0mph wall, you have to dissipate that energy upon deceleration. Carbon fibre shatters on impact, dissipating lots of energy turning the strong fibres into dust along thousands of fracture lines, breaking the bonds between adjacent molecules with some of that kinetic energy and the end result is a 'more controlled' deceleration. The skull will do something very similar slightly later, if it hits anything harder that a leather trimmed headrest.
But I digress.
So, our ideal 'necessary vehicle' is something like a Smart car, although the choice of powerplant (a turbo 3-pot) is a petrol. For such a utilitarian car, actually, the choice of power probably isn't too important - an economist might describe it as 'fuel elastic'.
But our sporting vehicle, well, that's a different beast.
I have often mused on how long it's taken the Americas to wake up about diesel. After all, the torque curve and power outputs of modern European big turbo-diesel engines very closely mimic that of the old musclecar pushrod V8s... perhaps the 1967 to 1969 Camaro Z/28's infamous 302 excepted.
And the modern turbo-diesel in medium capacity forms, as mentioned, has plenty of low-down shove, which makes for an entertaining ride in a rear-drive platform. It is merely 'mildly interesting' AWD roles, and when pushed hard 'barely tractable' in FWD.
However, I've driven 80s diesels where the 2.0 non-turbo was a better drive than the 1.7 turbo. This confused me a little but because it was diesel, I put it out of my mind... until I recently drove a turbo petrol car which has received rave reviews. And I have to say... I was underwhelmed. It seemed that I would push my foot to the floor, and the power was smooth, and the pickup was good... but as I got faster, it just became less entertaining... as the torque stayed the same, the power went up, but I didn't seem to be getting faster much faster. Very odd. This linearity of torque is actually (whisper it) quite dull.... compared to a VTEC petrol, for instance, which just gets more an more manic the more you psuh it, all the way through it's usable 6,000rpm rev range. It's putting the TDi's 2,500rpm usable range to shame, and the petrol turbo's 4,000 if you're lucky also equally humbled. And built for it, VTEC engines are actually more efficient that the arguably similar complexity in a turbo-diesel.
Now it gets even more twisted. Who needs 'flexibility' someone says - what about CVT transmissions? If you can make a CVT transmission with a high efficiency, then you can take any engine, set it at maximum power/volumetric efficiency and then accelerate at the maximum possible rate by adjusting the gearbox, not the engine speed. It would sound like an aircraft as it did so, which kind of takes the fun away in the sounds (dunno about you, but I made 'brum-brum' noises as a kid... who am I kidding, I sometimes still do) but hey, we're talking about efficiency here!
Ah, who are we kidding, we're not. We're talking about our opinions, what
we want. I want to tootle about in relative silence, but when I push the go pedal, I want it to build into an F1 like scream... then select the next gear and do it all again. I've driven turbo-diesels, and they're alright, but the 'drag-oops-change-pause-drag-oops-pause-change-repeat-until-in-sixth-and-don't-change-down' isn't for me. I want to row cogs on demand to have fun. I want to drop from sixth to third on the motorway and obliterate tailgaters. Horrendously antisocial, I know... but then all cars are, period.
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You must have not been in NYC to hear these in person. Same for tractor trailors.
What about Ford Australia? 
