Rust stands as the all-time champion in terms of code quality, both the language grammar and the tooling that rust’s community has built.
Rust can cross-compile easily (incl. exotic targets like wasm32-unknown-unknown), interacts with native code easily, has first-class support for lifetimes, and contains the second-best macroing system in the world (Zig’s comptime takes first place but has it’s own downsides because of how much it is used).
For any new systems of moderate complexity I find myself reaching for Rust because it has a large set of libraries, great tooling, and I know the compiler will make stupid mistakes nearly impossible which lets me focus on the design of the system without having to shoehorn in protections against null pointers & friends.
C is still relevant in 2020 because existing systems are written in C. For small, local projects C can quickly process whatever you need it to do (eg payroll systems, task managers, simulating economies at scale, and videogames).
For larger projects C must have additional tooling; look at what the linux kernel uses! If you have access to the tooling necessary there’s nothing stopping you from writing operating systems in C, but for now it’s primary purpose is to interact with and extend existing operating systems, which it does very well.
C is also relevant because it’s ABI is the most stable in the world; at the moment the C ABI is the only ABI respected by every language and every OS.
Python 3 is my all-time favorite scripting environment. If you need to process \~10gb of data across \~1000 3rd-party processes or remote systems, reach for 500 lines of python.
Python is also great for filling tooling gaps; I commonly have a build.py script where cargo and make fall short because building the project requires downloading a binary SDK which I don’t want to check into version control.
For small projects which use mostly 3rd-party tools on unix systems /bin/sh is great. There isn’t much to say about it as a language but everyone knows how valuable having portable shell scripts is and POSIX is the best standard that the world has been able to agree to.
These languages are nice when you have existing projects, 3rd party requirements, or for some reason the deployment plan just plays nicely with the language (eg existing Tomcat servers).
Otherwise these are strictly 2nd-tier languages.
“Nobody ever got fired for picking Java”
Java has runtimes for many platforms, a decent assortment of (aging) libraries, and enough tooling to make several nooses from.
Usually this is picked because of environment; there may be existing business logic in Java that needs a small extension, or you may have a deployment target that can use .jar/.war applications quickly.
C# falls into this category for me as well but I’m still learning it; C# appears to have better tooling available.