Looking for a bag

Hmm ok so im 5'5 and im 15 im looking for a punching bag.... I went to sport check and i saw a few bags there a 70 pound bag for $119 a hundred pound bag for $139 and a 50 pound bag for 139$ (its one of the ones that attaches to the ground and it comes with gloves and the clip to attach to roof and floor) o and they all come with the chains. I'm gonna be using them for just straight up boxing i might throw a few kicks into the bit just for fun but im not taking any martial arts or kick boxing.... Any ideas on which one i should get? :unsure:

Thx, Ian