Most unused defense of 2016?

[howdosheeplamp]

Since your alliance is forced to choose only 1 defense from each category, and your defenses should be as hard to breach as possible, it's seems clear that teams will pick the toughest defenses to cross. Some defenses seem harder to cross than the other in their category, and will probably be picked much more often than their counterpart.
What do you think will be the most unused defense of 2016? Personally, I think it'll be the rough terrain as it doesn't look like it'll slow down the enemy robots as much as the rock wall.
These are just guesses though, I have no idea what method of transportation teams are going to end up deciding on.