Walkers are Everywhere. Who ya got?
My money is on the middle distance runner, esp if he can do the steeple. Good mix of explosion and endurance. Only eats every other day anyway, so resource collection not a problem.
Triathlete may come in second (or first). Very good endurance for extended chases, and the ability to swim or ride could give him more options, although I am having a hard time envisioning the scenario in which either would come into play. Significantly weakened by lack of goggles, aerobars, or Bodyglide.
Putting Crossfitter third. Tons of muscular endurance and functional strength and may do well if climbing and lifting is involved. Weak cardio; will tire out quickly in extended chases. Already eats paleo, which will be all that is available.
MMA Fighter: hand to hand combat not advised against the undead. Will have limited cardio from general training, but his strengths are essentially nullified (unless competing against other humans for resources, which should not go unsaid.)
Sprinter: first to die. can only run in a straight line or occasionally veer left. Meaty. Delicious.
Remember: you don't have to outrun the fastest Walker. You only have to outlast the fattest sprinter.