You hit the nail on the head when you said - "... can be considered optimal for an orbiting rocket? By the combination of all characteristics."
The types of rockets vary by design, by crew size, by trip duration, fuel, by planned use, by payload, by any number of criteria. Are you going to Jupiter from Earth orbit, to Saturn from Earth's moon or are you going to Proxima Centauri from a Jovian LaGrange Point?
Space craft, in turn, may be powered by solid propellants, liquid fuels, nuclear energy, plasma, electric, thermal and by the solar sail system. Hence, a wide variety of propulsion types are available.
I hope the following helps to flesh out the types of propulsion systems available to you.
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In addition to the previous article on the Skyrora Company's 3D printing of a rocket engine for their SkyroraXL, which uses reduced plastic as a fuel called Ecosene, NASA engineers have also recently tested a 3D printed rocket part, named pogo accumulator, for their proposed SLS or Space Launch System, a small piece of hardware that absorbs the shock by regulating liquid oxygen movement in the engine. It damps the vibrations that can destabilize flight.
Printing pogo accumulator rather than manufacturing it, is actually a cost effective approach. By 3D printing the hardware, over 100 welds were eliminated, decreasing production time by 80% and cost by 35%. The hardware performed as per the expectations, and it also opened the possibilities for more modules scheduled for future tests.
Since each weld requires inspection and possible corrections, the reduction in the number of welds reduces the points of possible failure, labor and material costs. It also makes the engine hardware more reliable, the manufacturing process more lean and efficient and simplifies the supply chain while also reducing bottlenecks in the physical flow of materials.
See: http://propulsion-skrishnan.com/pdf/Classification of Propulsion Systems.pdf