I use this mobile from my freind and also in stores and I suggest to buy this 6 gb vareint.
Because the only difference between 6gb and 4gb varient is RAM and memory. And I think 6gb varient is GOOD for you. In 6gb vareint you never worry about space because of 128 gb ROM .
Your 128 gb Storage is enough for your data , movie , games, photos , pdf , music , and many more things what you want to store. So thats why I suggest you to buy 6gb vareint for your pocket.
And 48 mega-pixcel camera will feel you a professional camera.