Mountaineer FTW. I think both abilities are very powerful, but Mountaineer has a more cohesive concept behind it. I think Mountaineer makes sense. If you are familiar with mountaineering, you can avoid being surprised by rocks. That statement, in its base form, makes sense. Sure you can nitpick with questions like "How does it enable you to avoid getting hurt when the sharp edge of a stone is smashed into your head?" I'll answer that with another question, "How does levitating allow you to avoid damage and effects of a jet of mud shot at you? How about a bomb made of mud?" It doesn't make sense. But the general concept of levitation making you ignore effects on the ground -- that simple concept makes sense. Unfortunately, type immunities are not move-specific. For example, Ninty wouldn't say, "Hey, let's make levitators still get smacked with mud attacks, losing accuracy and all that." No, it's ground immunity -- plain and simple. Mountaineer is immunity to surprise rock damage (ie switching in). That fits.