This paper establishes some new links between the nonlinearity and differential uniformity of some large classes of functions, such as power functions, differentially two-valued functions and quadratic functions. We obtain a lower bound for the nonlinearity of general differential uniform power permutations, an upper bound for general differentially two-valued functions, together with some important results for quadratic functions. In particular, we show that the quadratic differentially 4-uniform permutations should be two-valued and possess the best known nonlinearity.