If your young and growing go 181. If your an adult or pretty much done growing the consider the 176.
will be good on rails. It's a matter of fast you can spin your ski.
Obviously a 176 would spin faster/easier to control cause less material.
A 181 would spin slower/ take more effort cause more material. But flip
side would be 181 more stable on big jumps/High speeds. 176 will be a little less stable.
I own last years AR7 176 and was on it pretty much on it all the time last season (cause not much snow).
Im 5'9'' 170lbs. The 176 felt great every where in the park but when on steep fast groomers I could feel the lack of stability. In the park I never hit anything over 15ft (I suck in the park) so really cant comment on jump stability. I had my skis at -2.5 and felt good every where. If I were to choose again I'd go 181. But keep in mind I ski 60%allmnt 40% park.