The benefit of waiting: more ability to accrue a down-payment.  Also don't unilaterally discount the value of a few more months.  I think it's worthwhile to find out how much you can get for your old vehicle at trade-in, if it's a non-trivial number, then you're better off pulling the trigger now than waiting.  The other factor to consider is how much free time you happen to have, if buying a new car is going to be a hassle with the rest of your life, better to get it done sooner rather than later when things are more complicated around the possibly non-functional car.

Generally speaking if you can get 20% down you'll greatly increase your odds of being approved, 30% is pretty much guarunteed... I got my financing with a worse credit profile than what you have currently from the sounds of it.

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Starting Score: EQ 561, TU 567, EX 599* (12/30/11, EX lender pull 12/29/11)
Current Score: EQ 660, Wally TU 697, EX unknown (05/13/13)
Goal Score: 680 in all three (01/01/14)

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