What size snowboard!!!!!!!???

Im 5'7" and a half and my weight fluctuates a lot. i can go from 135 to 150lbs at times. according to the burton board finder if i weigh 145 im a 155cm and if im 137 then im a 152cm. Which one should i go with??? my skill level is beginner/ intermediate by the way. I would like to do some park stuff in the future, but i want to improve my speed as well.