A hybrid or diesel. Diesels burn very, very little fuel when unloaded (e.g. at idle) compared to gas engines.

That's the idea there. A diesel has a nearly unlimited air fuel ratio range. Gas engines can vary their air fuel ratio by moving the throttle to increase or reduce the amount of air going in the intake, and then the carburetor either squirts in more fuel or the injectors fire longer to compensate, based on the manifold pressure, rpm, and other factors monitored and adjusted for by the computer controls. Diesel engines are ALWAYS at full throttle even when your foot is off the pedal. What you're varying in a diesel with the pedal is the pressure used to open the injectors.

*footnote, newer diesels with EGR do have a throttle that can change airflow to create vacuum to allow the exhaust gases to recirculate for emissions reduction (NOx mostly).

A gas engine can vary its air fuel ratio from about 8:1 (very rich) to 18:1 (very lean). A diesel engine, however, varies from about 5:1 (very rich, under full load, accelerating) to as much as 100:1 (idling, no load, so lean it qualifies for the American Heart Association Lean Meat seal of approval)

Get a diesel and make sure to remap your ECU to fit your specific needs, which in this case is to make the fuel to air ratio as lean as possible.
If remapping ecu, buy a car that is out of warranty. And before buying, do an online research for the most common problems that that particular model will have (something you can't do with vehicles), and ask your mechanic how much will they cost to repair if they arise.
If the car is equipped with an automatic shutdown when stopped, make sure that the restart is NOT done with the starter motor because they tend to wear out very quickly.

I'd also get an automatic diesel to make the commute less stressful.

Don't forget your climate. Generally, when the engine stops, so does the heating and/or air conditioning. I'm not sure, but maybe some hybrids can run the A/C compressor electrically for a while. If so, the engine still has to recharge the battery.

My new car which I pick up at the weekend, is an ecodiesel, the technology involved is amazing and it offers much better economy and lower emissions than a hybrid. It also has the stop start feature so when waiting in traffic, then engine stops. Pop the clutch in qnd it starts instantly. Not sure how it works, but all the electronics and ac continue to work. Amazing stuff.

I wonder how lesser manufacturers like GM will fare with starter reliabilty once they incorporate stop/start technology? I imagine this may be a problem for some consumers & negate any fuel savings once the starter needs replacement.

GM has had stop/start technology in regular production since at least 2004. With ten years of data, it should be easy enough to determine. I know the 2004-2008 Silverado hybrid had more specialized equipment, but since 2008 I believe they've been using more common equipment, though probably still not the standard starter from a non-hybrid.

Stop-start technology is old and well-understood. Golf cars have been using it for decades, although fuel economy was not the reason.

There are cars that stop the engine at a specific crank position. Upon restart, a small quantity of fuel is injected and burnt, restarting the engine.
I'd take that system over any electrical-restart one.

That is Mazda's system.
GM's adds a deep cycle battery in the trunk to run the accessories on stop to preserve the starter battery.