At a node, currents $I_1$ and $I_2$ enter, while $I_3$, $I_4$, and $I_5$ leave. Which equation correctly applies Kirchhoff's Current Law?

Kirchhoff's Current Law says the sum of currents entering a junction equals the sum leaving it. Since $I_1$ and $I_2$ enter and $I_3$, $I_4$, and $I_5$ leave, the correct relation is $I_1+I_2=I_3+I_4+I_5$.