More pros with a mobile, usually makes people more directly reachable wherever they are and even if they can't get through then the missed call will show up wherever you are with your mobile, there is almost always a voicemail function (moreso than landlines) and the number is stored automatically if shown. It's also more private as less chance of getting someone else, especially if anything sensitive or confidential.
I would automatically go for a mobile number unless I had been told otherwise.
Things can move quite fast in the recruitment world so getting hold of candidates quickly can be important, especially if there is competition, as if you don't fill the vacancy then you don't get the fee.