Do you do any serious coding in either?
https://www.bitdegree.org/tutorials/c-sharp-vs-c-plus-plus/
"...However, specialists believe that the differences in the C# vs. C++ performance are minimal and exaggerated.
The speed of programming languages is not always the priority. If you can reach your goals much faster in C#, you do not need to spend more time trying to figure out the principles of C++. ..."
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Of course, if you are already skilled in C++, use it.
I know that most here are using servers one block from the exchange, and are trading in microseconds, and are writing their own trading strategies, and thus should use assembly/C++/C for all their stuff.
The rest of us should go with what's easier, and quicker to code/debug/update, as long as it's fast enough for the individual needs and trading strategies. K.I.S.S.