Snowboard question!!?

Im buying a new snowboard (yay!) and ive have my mind made up about 90% that i want to get the roxy ally. The problem is i have to choose between a size 148 and a size 151.. I know everyone says to pick a board that is between your chin and nose but your also suppose to keep your weight in mind. a size 148 comes just below my chin but im pretty lightweight, and a 151 almost touches my nose. So which one should i go with? I just want to make a sure desision before i spend my money on a 300 dollar board. oh and if this helps any im 5'5" and i weigh 108 lbs. oh and id love t hear any other advise you may have on picking a board...(keep in mind im at about an intermediate level, i like carving, and i might want to learn some jumps..) but mostly--what size board should i get??