Whether the better way of expressing it is litre/km or km/litre depends on whether you are trying to work out how much fuel you need to get from A to B or trying to work out whether you can get from A to B on one tank.
With the ready availability of pocket calculators, the practical difference is zero - the only advantage of either method is that most people can multiply in their head easier than they can divide.
(Since you are buying fuel in litres, if you have a speedo in km, which is everyone except early Series owners, miles don't come into it, and /100km is a bit silly as well).

As I said above - there is no real advantage to either, it is simply that some people are more familiar with what they grew up with. For example, I grew up with the idea that a reasonable fuel consumption figure is 30mpg (9.42l/100km), this being the sort of figure you got from a Holden (48/215) or my father's Swift, and consequently I use it as a yardstick to this day, so I have to convert either way to compare. But I don't think that either method is inherently better, although I do think the 100 is silly - it is there only so you deal with whole numbers, and the simpler way would be to just use km/l. The argument over whether a smaller number is better or a higher number is better simply depends on whether you are playing golf or cricket - and seeing that we were used to having a higher number as better from the start of motoring, and the rest of the world still works that way, it is simply a change to be different foisted on us by the metric conversion board.

John

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JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol