There are two measures with a rocket engine.
Firstly there is thrust.
Then there is fuel consumption.
With conventional rocket engines one is inversely proportional to the other. Thrust means you cannot achieve fuel consumption efficiency as the exhaust velocity is relatively low.
You want a lot of thrust when you launch from Earth as you have to push your entire rocket up against gravity, and quickly enough that it doesn't topple over when you lift off the pad; consequently you want to shove as much propellant mass out of the nozzle as possible, even if you don't clean burn the entirety of your propellant. Rocket nozzles are optimized for certain flight regimes and the first stage is usually burning most efficiently not that far from the pad.
This is where the kerosene/RP1 comes in for big lifting because it is vastly denser than that other major rocket fuel, hydrogen.
Fuel consumption kicks in when you are at altitude and moving fast. You use your second and subsequent stages to burn much lighter propellant, such as liquid hydrogen.
The critical value here is exhaust velocity. The hydrogen, being as light a molecule as you can get, is kicked out at a much higher velocity and so is much more efficient as a fuel - the efficiency is measured as the log of the exhaust velocity.
The downside is the thrust is small compared to the Kerosene/RP1 propellant and your LHyd/LOx rocket may not even have enough thrust to get off the ground, so is useless as as first stage.
One way round the thrust/efficiency conundrum is to go nuclear. You can shove the hydrogen fuel out the reactor nozzle at ludicrous velocities, hundreds of times more efficiently as a chemical rocket and get big thrust as well.
The problem is that as soon as you mention nuclear some people start frothing at the brain and automatically hitting the downvote button.