I would advise to go with a bit longer ski. When your hitting jumps (particularly larger ones that require a faster drop-in) the added length of a longer ski will feel much more stable. A short ski will get somewhat jittery at higher speeds and may make you feel less stable thus inhibiting confidence.
However, only listen to that first point if you consider yourself to be an experienced skier. If you are just getting into it, a long ski can feel a bit overwhelming and may make starting out a bit more difficult.
So like most things, it really does depend...