I. Kant is hard to understand. I like philosophers who are hard to understand because we must increase our capacity of attention when we read their works. Nietzsche is also hard to understand, but he would make you believe that his writings are easy because they’re written in a simple style, using no complex words, so everybody thinks they’ve understood Nietzsche. Nietzsche’s writings, however, have to be considered all together and even then you find a lot of contradictions in them, which I think Nietzsche did deliberately because he despised all kinds of systematic thinking. To reproach Nietzsche for being too contradictory, like many people do, is to prove that one has not understood the man.
I guess all philosophers are difficult somehow. It’s already difficult enough to try to understand anybody else’s ideas. So when it comes to philosophers, the difficulty increases a lot more because their ideas are much more developed and reasoned, and we only have their literary legacies to approach them. And language is a very elusive tool, a rather imperfect vehicle to approach reality. I’d say your question is difficult because in order to pick up one favorite philosopher, you have to be really sure you understood every one of his ideas and their implications. I guess I could not give a straight answer. Plus, then comes my belief that philosophy is an organic body, every stage of it being equally important than the others.