The primary difference between these three technologies is the fragments of interest. In 3C, you are probing for an interaction between two specific regions that you identify a priori. In 4C, one fragment of interest is known, and you probe for all the potential fragments interacting with your fragment of interest. Hi-C is an unbiased method that can identify all potential fragment interactions without any a priori knowledge of the interacting fragments. The review cited by Katrin is indeed one of the best if you're looking for a general description of the various methods.
Article De Wit, E. & de Laat, W. A decade of 3C technologies: insigh...