The two routes are about the same in term of distance and time. Both are on divided toll motorways managed by the same company (Autostrade per L'Italia SpA) and you will not be driving within cities either way, just freeway all the way until you exit near you destination.
If you go to Monterosso, the route via Genoa (A7/A12) is a handful of km shorter. In that case the exit on the A12 is Levanto. If you go to Riomaggiore then the Parma route (A1/A15) might be slightly shorter, but it's really minor differences. In the latter case the exit is La Spezia and you drive through La Spezia to go to Monterosso. In both cases the freeway goes through mountain ranges and in both cases you will be driving through freeway tunnels, although the Genoa route will have more. But they are well lit, so no reason to be scared of the dark. I've traveled all those freeways, and the one via Genoa is more fun. If your destination is Monterosso, I'd take that one.
What might make the difference in driving times is car accidents or road work along the way, which one cannot predict and it can affect either or both routes.