Answer
a) is correct.
Work Step by Step
Let's call the holding force from our hand $F$. Because $F$ opposes the suitcase's weight from making it fall down, $\vec{F}$ points upward.
The work done by $F$ is $$W=(F\cos\theta)s$$
When the elevator rides up, $\vec{s}$ points upward as $\vec{F}$, so $\cos\theta=\cos0=1$, meaning $W_u\gt0$
When the elevator rides down, $\vec{s}$ points downward opposed to $\vec{F}$, so $\cos\theta=\cos180=-1$, meaning $W_d\lt0$
Therefore, a) is correct.
