I just joined this forum but have a bit of experience.
Will depend on snow conditions and riding style.
A longer board would be good to start and learn on groomed conditions.
A shorter board possibly once you get better?
The longer boards will tire you quicker and more so as conditions start to get choppy.
A shorter board will cause less fatigue yet needs a bit more skill.
AS you have been on the slopes alot do you have friends who board or friends with kids who ride?
Do any of them have boards they could loan you for the day to see how you like them?
I would suggest staying below a 157 and above a 145.
Boards have different degrees of flex and sidecut and that is a consideration too.
I am sure there are many posts on this subject and a search may help you find the answers you need.
Try advance search with just 1 or 2 keywords in thread title only.
Here is one from earlier I read that may help.
Just click on the link below.
Is my wide board holding me back?