In this work we study preference systems suitable for the Peer-to-Peer paradigm. Most of them fall in one of the three following categories: global, symmetric and complementary. All these systems share an acyclicity property. As a consequence, they admit a stable (or Pareto efficient) configuration, where no participant can collaborate with better partners than their current ones. We analyze the representation of such preference systems and show that any acyclic system can be represented with a symmetric mark matrix. This gives a method to merge acyclic preference systems while retaining the acyclicity property. We also consider properties of the corresponding collaboration graph, such as clustering coefficient and diameter. In particular, the study of the example of preferences based on real latency measurements shows that its stable configuration is a small-world graph.