Originally Posted by rillenn
Well you're right but this will be my first rockerskies and I'm thinking that because it's rocker it should "behave" shorter, right?
You are right about that. @beyond has the core decision framework pretty well pegged here.
Based on your self-description I'd say go 180, especially in the Alibi which is a pretty light feeling ski to begin with. If you are a pretty strong skier, if you're talking about pushing into the backcountry, you would likely find the 173 to feel really short and maybe too insubstantial for anything except tight spaces and quick fall line turns.
It depends a bit on your location, purpose and style - based on what you have said, I'd go with the 180 in this ski. I wouldn't worry about it, but if you are super worried about length, and you like the idea of the Atomics, you could consider the Ritual at 174, which would probably deliver more stability as an all-mountain ride in the 173/174 length slot without a major weight penalty over the Alibi.