In modern smart grids, prosumers and distributed energy resources increasingly participate in local electricity markets, while higher renewable penetration raises the need for reserve capacity and operational flexibility. This paper proposes a joint peer-to-peer (P2P) market framework for energy and reserve trading with product differentiation, in which agents negotiate bilaterally with neighboring peers and can trade both energy and reserve capacity. The resulting social-cost minimization problem is formulated and solved using a centralized benchmark together with ADMM-based decentralized and distributed clearing mechanisms. In the fully decentralized market, a coordinator-free consensus ADMM is adopted for direct P2P trading, whereas the hybrid framework employs an exchange ADMM to clear intra-community trades prior to decentralized negotiations across communities. Numerical studies quantify the trade-off between centralized and decentralized clearing in terms of objective value, computation time, and communication burden. The results further demonstrate how product-differentiation coefficients influence market prices and traded quantities. Finally, two coefficient-setting strategies are introduced to steer decentralized market outcomes toward centralized-like or hybrid-like operating points, thereby enabling the market operator or platform designer to influence trading behavior under decentralized clearing.