I had to vote the dreaded "other" on this one.
The title of this post asks the question "which do we PREFER", to which I would have to answer blowjob. That is followed by "which gives more SENSATION", to which I would have to answer fleshlight.
For me the sensations created by a Fleshlight are almost always more intense than those recieved by any sexual act. But, I would never take a fleshlight over the real thing. It is a fantastic replacement for your hand, but other than that the real thing wins out every time.