What's the best way to create a new zero Vector3?

I need to create a new Vector3 with 0 in all position to sum a list of vectors and mean them. What would be the best way to start it?:

Vector3 sum = Vector3.zero;
Vector3 sum = new Vector3();
Vector3 sum = new Vector3(0, 0);
Vector3 sum = new Vector3(0, 0, 0);

I will be using this sum like sum += otherVector, so what initialization would be best? I guess the options 3 and 4 should be the same, but what about 1 and 2? Does 1 create a new vector for use? Can I assume that option 2 will create a vector with zero in all fields?

1: is a bit slower because it’s a property inside Vector3 class.
2: Vector3 is a class and a default constructor initializes the members with their default values (0)

performance wise: instead of assigning one unnecessary value just use the first relevant one. if referencing a static readonly field or using the constructor every time is faster, I do not know.