Nikon d750 oe sony A7ii which camera can i buy? so confused,

Here's some questions that will help determine what is good for your needs:

1) Is size important?
2) How long have you been taking photographs?
3) If a scene is F4 1/100s ISO 400, what would you need if you wanted to bump up the shutter speed to 1/400?
3b) If you don't know the answer to #3, are you interested in seriously learning photography to solve it for yourself?
4) Do you have any camera equipment already?
5) What are your primary focuses? (sports, landscape, animals, etc)
6) What is your budget?
7) Are you trying to buy a tool or status symbol?