You're going to get a variety of responses here because everyone has a different point of view on this.
Rationally, it makes the most sense to pay down the loan with the highest interest rate. If your student loan is being deferred (and assuming it doesn't accrue interest during this time), then the mortgage is where you should be putting your extra money. Then when the student loan kicks back in, that's what you should pay down most aggressively. Save the low-interest
My own personal preference (I am not always rational) is to pay down the easiest one first, which is probably the car payment. Or even the student loan. Because I hate having multiple sources of debt more than I hate paying a little more in interest.
Others will tell you do none of these and instead invest all surplus cash since the interest rates are lower than what a market index fund generates, on average, per year.