If you're gonna be riding a lot of park, it comes down to preference on whether you like a longer or shorter ski. I don't speak from experience, but I assume a shorter ski, like 164, would be much more maneuverable, making spins easier. A longer ski would be more stable on rails and carry speed better in the pipe. It's up to you.
As for all-mountain, that is rather short for a ski like that. I doubt they have any metal in them and probably aren't all that torsionally stiff. To get the stability you need, consider a longer ski. That is, if you ski aggressively. If you're just getting into it, 164 should do fine.