Fuel efficiency

which makes the most sense if fuel efficieny is your goal: hybrid or disel?

Where will you be doing most of your driving?

If most of your driving is in urban areas, a hybrid would be the likely winner.
If you do a lot of highway driving, a diesel engine would probably use less fuel.

Ask them to build you a hybrid diesel…65 MPG no problem…And because the diesel engine can be tuned to run at a constant load and speed, it can be made VERY clean running…

But what to do with all that gasoline our refineries are optimized to make…

Chrysler came out with a diesel powered hybrid about ten years ago that got over 70 mpg. It was the size of a Dodge Stratus and had decent performance, but never went into production because the EPA said it polluted too much. Makes sense. 70 mpg but it’s not as clean as we want it, so no go.

Well, there’s a distinction between “clean” and “fuel efficient.” I could power a bicycle with a 2-stroke chainsaw motor: very fuel-efficient, but pollutes* more than an H2. Diesel is more efficient, but dirtier than gasoline.

(* This asterisk is only necessary because the EPA chose to define CO2 as a “pollutant,” so that they can regulate it. This flies in the face of the traditional definition of a “pollutant” as something “harmful or noxious in trace quantities,” and is similar to the DEA defining every illicit drug as “narcotics” so that they all fall under the Harrison Act.)

Neither, as making fuel efficiency your only goal is a fool’s quest. You might as well look for a house and consider only those with a metal roof, regardless of location. Hybrids as stated are too restrictive for both vehicle type and use and diesel prices are too volatile. There are also too few diesel vehicles offered to give you good price and performance competitive options. Right now, IMO, the smart thing to do is get the highest mileage gas vehicle in the lowest price car with the best repair record (a real cost saver) in a vehicle that suits all your needs. Getting good mileage (hybrid or diesel) on a car that cost too much to begin with or spends too much money/time in the shop or doesn’t meet your needs otherwise is not a worthwhile $$$$ saving option.

Neither, as making fuel efficiency your only goal is a fool’s quest.

I would not have made the assumption that the OP has made fuel efficiency the only goal. The OP asked a very basic question about which one does a better job of achieving the goal of high fuel efficiency. Nowhere did the OP state that it was the only criterion in her/his selection of a car.