Having the lower resistor about 10k will be more power-efficient and isn't too large
for the ADC. 10k and 33k would divide by 4.3, 10k and 22k would divide by 3.2
You can use larger resistances (might be useful if you want to avoid long term
current drain), but you then should add a 0.1uF capacitor too to reduce the impedance
seen by analog input (otherwise readings can be rather off the correct value).