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The PIC18F45K80 has a built in ADC, and that would be the easiest to use.
Almost all ADCs work best with a signal that changes over most of the range of the supply voltage. The PIC18F45K80 will probably be running from 5 V, so the ADC will work best if the signal from the sensor covers a good proportion of the 0 - 5 V range.
You don't say what the range of the humidity sensor analog signal is, but if it's not a voltage in the range 0 - 5 V, and it if doesn't change by more than about 1 V in the humidity range you are interested in, then some sort of signal conditioning would be needed or would help.