Should I get a size 155 or 158 snowboard?

I'm looking into buying an arbor formula snowboard but not sure which size is best for me. I'm still a beginner, I'm 6 feet, 155ibs, and have a size 10.5 boot. Should I get the 155 or 158? I know going smaller would probably make it easier for me but the 155 has a 25.1cm waist width, and the 158 has a 25.2cm waist width so also not sure which width would be best so i don't have any drag. Just looking to use this board to get better with and maybe eventually trying out some park stuff.