That depends on personal preferences. I personally love both techniques so both are equally difficult/easy but they're both of course very different so something that can be easily achievable with digital techniques can be very difficult to do with traditional media and the opposite.
I think digital art requires much more work and skills to get the same appreciation from the audience as slightly worse traditional artwork would get. So in this meaning, you can say that digital art is harder. But then, on the other hand, there is no "undo" in traditional art :)