Beginner Surfer, What size board should I get?

Question

Hi, I learned how to surf longboard in like 3 foot waves, but I really want to get into shortboards. I'm 5'7, 150 lbs, strong swimmer and pretty good with balance from snowboarding, and up till now I've been body boarding quite a bit.

anyways, does anyone have any advice on what size shortboard I should get? and roundpin or fish?

Oh and I'll probably be surfing about 3 days a week.

Thanks a bunch guys