Answer
$$N{O_2}^- \space is \space the \space stronger \space base$$
Work Step by Step
1. Compare the strength of their conjugate acids:
$HNO_3$ and $HNO_2$
Since $HNO_3$ has a greater number of oxygens, and electronegative atoms connected to the central atom ($N$) are responsible for raising the acidity, this is the stronger acid, and $HNO_2$ is the weaker one.
2. The stronger the base, the weaker its conjugate acid. Thus, we can affirm that $N{O_2}^-$ is the stronger base.
