Personally, with brake trouble you are having, I would have replaced all 4 rotors if replacing the pads all the way around. Why cheap-out on the part of your car that does most braking? Your front brakes do at least 80% of your stopping the car. Generally, the fronts will warp before the rear. There are exceptions.

Good luck, James

PS Vibration from the brakes is not always from warpage. You could have hard spots in the metal (rotors) causing the same symptoms. Sometimes it can be seen, and sometimes not.