小弟想买一部macbook air 做功课 ,各位brother比d意见

小弟想买一部macbook air 做功课 ,各位brother比d意见  or 或者等6月Apple 好似会系WWDC 发布新一代LAPTOP
BTW I need some comments
Which one is better

13 吋 : 128GB
1.8GHz 双核心 Intel Core i5 处理器
Turbo Boost 快达 2.8GHz
4GB 记忆体
128GB 快闪储存 1
Intel HD Graphics 4000

13 吋 : 256GB
1.8GHz 双核心 Intel Core i5 处理器
Turbo Boost 快达 2.8GHz
4GB 记忆体
256GB 快闪储存 1
Intel HD Graphics 4000

which one is better, because i just use for watch youtube and download some movie.

i just use for watch youtube and download movie . Is that has enough gb for me , because I'm not sure this is my first time to get a apple laptop. I even use apple before.
btw thanks

do you need a MBA or you just want a MBA?
e.g. I own a MBP because of programming
if you just use MBA for watching youtube or movies
I don't think you have fully utilized the function
you should be also noticed that there are many software cannot be used in MAC OS