C is good for a lot of things, but does expect you to be able to program a lot of things from scratch.
Python for Switch seems to be good for filesystem tools, as it doesn't have access to much else.
Lua for Switch is capable of doing a lot of things on Switch, but whether or not C libs are usable on the switch in the context of Lua would be a defining factor in whether or not this as useful as using C.
JS for Switch isn't complete yet, but it doesn't have much access to the Switch outside of the SD card filesystem.
Out of these, I would recommend C if you know how to program using it.
If you just want to use Lua for some basic stuff, I'd recommend giving Love Potion for Switch a shot.