Be sure to use normal maps! Diffuse is just one of many components that go into a material. If you're using only diffuse, you're using only 1/4 of the material's potential, and at best 1/3.
thats because you havent got a shader applied to the diffuse... throw it into your favourite renderer with a normal map and crank up the reflection. it'll instantly look a lot less like concrete!
Thanks for your answer ! I was persuaded that a good texture was mainly thanks to the diffuse. I think that the first one looks good, but that's not really the case of the second. It looks too "perfect". (I work with UDK )