The Wolverine. Few of the X-Men have a reputation for hunting that rivals Wolverine. Logan's senses operate at a heightened level, and once he's got the scent of an enemy he just can't be tricked.
Except, of course, by telepaths. A good psionic can get inside Wolverine's head and mess with his senses, leading him on a wild goose chase. During Marvel's "Onslaught" saga in the '90s, the psychic monster created by combining the psyches of Magneto and Charles Xavier proved able to go one step further. Onslaught was literally able to deceive Wolverine's senses of smell, sight, and hearing, operating with impunity without Logan even knowing he was in the room. Xavier had explored the minds of his X-Men on many occasions, and as a result, Onslaught appeared to find it easy to do.
There was, however, one X-Man who couldn't be fooled. Iceman figured that Onslaught would be messing with their perceptions, and so he concentrated "on seeing everything only in of body temperatures." It seems Iceman has a secret super-power, one neglected by many writers; he can perceive the world through temperature. Imagine him as a tracker, locking on to a person's body temperature and monitoring them with ease. In the case of Onslaught, he was on to the menace the moment he walked in the door and waited until he was carefully positioned before springing a trap.
Iceman is an Omega-level mutant, meaning there is essentially no limit to his potential power. While he tends to focus on direct ice manipulation, comics have hinted at far more diverse abilities, including Psylocke learned once when she tangled with Daredevil.
This certainly means Iceman has the potential to be a far better tracker than Wolverine, simply because his heat sense operates in a manner that is far more difficult to deceive. If he's tracking a target, he'll be able to perceive the trace heat they leave behind as they move through the environment, every trace of their exhalations. There really are hidden depths to Iceman's powers.
