Cruise control usually returns better fuel consumption for the reasons given above; it can use more fuel in certain conditions.
Letting your speed bleed away a little on short and gentle inclines and using the down slopes to build momentum will use less fuel than cruise control in a similar situation.
Cruise control will use a wider throttle opening and use more fuel going up the hill to maintain the set speed, going down hill the cruise will go to the other extreme and almost shut the throttle - but significantly it will rarely close the throttle totally. The extra fuel required to build up momentum again of the downslope is less than was used to hold the speed going up the hill.
The difference is more noticeable on less precise vacuum controlled CC systems. I prefer to use CC myself though.