Let me clarify here. A Polo does around 65mpg. Your Alto supposedly does 50mpg. I find this extremely difficult to believe, what with your 160km/h jaunts and your... addled... driving reports. Diesels can usefully extract the maximum economy- having driven an Audi with the 1.9TDi, I was getting 53mpg on the motorway whilst doing 110mph. My little Peugeot, no matter how I drive it, manages AT BEST 38mpg overall.
I agree with your first statement, neither are perfect. I'd say the petrol engine sucks for changing conditions. I ran into traffic today and my instant consumption dropped from around 42mpg to 30mpg- used over 3 litres of petrol for 1.2 miles of traffic, doing nasty things to my clutch. When I did the same thing in a diesel Auris, I was doing 46.3mpg in traffic, and 50mpg on the open road with a lot of fast downchanging and basically driving like a nutter.What everybody seems to forget though is that neither of the engines is perfect. A petrol engine for example is best in changing conditions, while a diesel is best in long running around the same rev range, for example Autobahn driving.
You also forgot that petrols emit much more CO2 than diesels. How do you mean by elasticity? Unless you have a petrol engine with a rude amount of torque, you're gunna be changing gear a lot more than with a diesel. High torque and a useful rev range allow for you to stick in one gear more often with a diesel.Petrols are less fuel efficient than Diesels, but usually have a bit more "elasticity". Diesels emit more NOx then again...
Diesel seems to be the 'better' fuel at the moment, it's cheaper than petrol here and lasts much longer. A Peugeot 306 DTurbo gets around 550 miles to a tank of diesel, the equivalent 1.6 with a similar amount of bhp and much less torque pulls around 330 miles to a tank. The diesel also has an excellent midrange flexibility for quick overtaking, very useful in the real world, and they cruise nicely. The only realistic penalties I can think of are that it sounds like a tractor and doesn't have the same handling sparkle as the lighter petrol model.This argument will never be solved here, as everybody has it's personal preference. The individual engine types both have drawbacks and advantages. One weighs up against the other and because of this a decision can never be reached. It's as simple as that.
You're looking in the wrong places. Considered something older? And what the hell do you mean by 'they provide a nicer ride'? Try telling that to a Maybach or Rolls-Royce Phantom owner- both petrol, last time I looked. Also, a petrol will deliver handling less likely to understeer- less torque, less weight over the front axles- therefore making it a preferable drive.My personal preference lies with Diesels as they provide a nicer ride IMO. Because i drive almost 500 km a week (most highway), a diesel would also be the cheaper solution for me. Purchasing price is what stops me.. I also feel the Diesels have more development ahead of them. Just look at the ease with which some manufacturers achieve the Euro 4 &5 norms, even without particulate filters...