Who walked the most steps is not always the best way to award your walkers. In fact, it's often a way that might discourage those who deserve being awarded the most such as those who made tremendous strides during the course of the program or who picked up a life-changing habit of a higher level of physical activity. Your top steppers probably had very high physical activity levels before your program started.
In light of that, here are a few other metrics with which to give merit where merit is due:
Walker Tracker Points: In your administrative panel under 'statistics' you'll find 'Point stats'. Walker Tracker points take into consideration a number of factors -- diligence, how often you're hitting your step goal, if you've received points from others, if you've participated in forming a healthy program. It ignores step totals -- and so it might be an excellent metric for pulling out who gave the program their all.
Consistency Award: For team competitions -- look for teams whose averages are consistent across all walkers. This would award the team whose individual averages were closest to each other – i.e. the smallest % difference between the high and low average on the team.
Just in Time Award: Award the team and/or individual that is closest to the 10,000 step daily average. You could do this along the way at selected milestones (e.g. 1/3 the way, ½ way, etc). People closest to the 10K average will arrive at the destination just in time.
Carrying the Water Award: This would go to the individual with the greatest contribution to her/his team results. (the % of the team total that is due to that individual).