I see this question a lot and durability is hard to measure as everyone skis their skis differently and there is no real way of doing standardized tests. Sure there will be brands who are generally better than others with care and attention to the quality of product they put out and the only way to find out that is to ask the end users.
Hopefully the new review section will help give a general idea of what companies and skis are worth the money and so there will be less need for threads like this, but until then look out for companies that tell you more about what materials and work goes into their skis because that shows that they take pride in the quality of what they're producing.
A common example of this is the series of ptex sintered base which is on the ski, the higher the number (in thousands is) generally the more dense the base material, so will take less surface damage from rocks & rails etc.
Personally I cant stand when a company won't tell you much more about a ski than a short marketing spiel. yes, there is a place for technical info and its not what everybody wants to read through when picking ski but its generally better