You can add automatic versus manual transmission to that list these days. I know there are purists out there who will argue that manual transmissions give them "greater control" over the vehicle, which is just bollocks in my eyes, but the fact remains, a well designed modern automatic transmission is better than old manual boxes in every way, including fuel economy.
I have yet to see one automatic transmission that doesn't add at least 0.5l/100km
Then you haven’t looked at cars in a
very long time, and/or haven’t looked carefully enough.
It’s honestly kind of hard to compare with most cars, because they often don’t let you choose the transmission without also changing a bunch of other stuff at the same time, whose weight differences invalidate the transmission comparison.
But for example, in the BMW 1 series, where you actually can choose multiple engines and transmissions independently, only on the 116d does the manual transmission
potentially save fuel. And I say potentially, because only one end of the consumption range changed, and only by 0.1L/100km. On every other engine type, choosing automatic either has no effect whatsoever, or
reduces fuel consumption.
This is how it’s been for many years now.
The reason manual transmissions used to be so much more efficient in the past is because they had more gears than automatics. (E.g. in the 80s, a compact car might have a 5-speed manual, but only a 3-speed automatic.) But we now generally have the same number of gears in an automatic (6 being really common now), and a smart computer deciding when to switch. That computer will, on average, do
better at switching gears than an average driver.