Replying to What size ski's do I need?

Hey I'm planning on getting some line anthem's and they come in 161 and 171. I am about 5'7, 150. I have only skied once, so I  am a beginner. I plan on riding park with them after I get the swing of things. I want the 161's because ill be riding park but all mtn. as well. Im probably going to outgrow the 161's real quick but I feel the 171's might be to big. So what size should I get? Does anyone know how they the anthems do all mtn. also?