Anything that is good to do is a mitzvah (The other choice is an aveira)
You missed one – the third choice, which is neither a mitzvah nor an aveira. (This is known as the fallacy of the excluded middle).
For example, the choice between eating a tuna fish sandwich or a peanut butter and jelly sandwich. It’s my option which to choose and neither choice is a mitzvah nor an aveira.
The Wolf