Based on your question, it sounds like you're wondering which salary would be the "primary" on a joint tax return. The answer is neither. It doesn't matter which salary is entered first or second. When I file our taxes, I put my info first because I get it before my wife's comes in. It used to be that her info arrived first, so I entered hers onto the tax forms first. It's a joint filing, not a primary with secondary.
You're not adding salaries together. You're filing 2 separate salaries on the same form. For each salary (assuming not self-employed), you should each have a W-2 at the end of the year to enter.
However, there is a general recommendation to keep it consistent year-over-year: Significance of first name on joint tax return