better off using higher value resistors to reduce the over all current draw of the voltage divider , but if you have too higher values the current will not be enough for accruate reading but after you do testing you will find the avg voltage range with the resistors used and you can apply that offset to the reading.

also use the inbuild voltage ref for the ad readings so that when you transfer between various input voltage on differnat pics , the same code and voltage tables can be used for either 10 bit or 12 bit ad cpus