new board

im looking for a new short, im 5'11 live on the westcoast weigh 145 and 18 id say im intermediate but my boards stopping me from advancing with riding the line fast and doing snap backs i just wanna get a good idea of what shape size and liters i should get my board we get 5- maybe 6 foot sets on a real good day but its usually 3-4.5 footers but im planning on taking more eastcoast trips so i need help