Actually, that's not an array, it's an object literal. A better comparison would be a Map, not an array. In your example, data is an object that contains 2 properties, ipSTID and ipSVID. With the first approach, you're assigning values to the individual properties of data. With the second approach, you're replacing the entire data object with a new object literal (and incorrectly including the "var" keyword again). The second method is riskier because you're replacing an entire object. In general, the first method is the one that I think probably makes more sense for most scenarios.
I generally agree with what you're saying. I would choose the first method (assigning values to the properties of the object) rather than the second method (assigning an entirely new object to the variable) in most cases. Of course, there are exceptions to every rule and it probably depends on what you're trying to do. For example, there may be cases where you WANT to replace the object. Neither method is really incorrect, it's a matter of finding which method is the most correct for your situation.