© 2013 IEEE.This paper studies the problem of optimal cache placement to maximize the offloading probability in a device-to-device (D2D) enabled cellular network with small base stations (SBSs). Different from most existing works, we consider unequal users' equipment (UE) cache memory sizes and all wireless links are modeled as Nakagami- $m$ fading. User preference for each UE and global popularity for SBS, as well as the higher priority of content request from neighboring UEs vs. SBS, are the main factors that make the problem formulation of our work different from that of existing works. It is assumed that each UE caches its desired content with the order of searching its cache, neighboring UEs' cache via D2D communications, and its serving SBS' cache. A close to optimal low complexity heuristic cache placement policy is proposed and it is shown that its performance reaches the optimal caching strategy.