Peer-assisted systems that use BitTorrent-like peer-to-peer protocols can potentially support on-demand streaming of popular media files to large numbers of clients. In these systems, the policy used for exchanging content pieces among the participating peers is crucial to system performance. In this paper, we present an evaluation of two candidate piece selection policies, namely Portion [1] and In-Order, using an instrumented BitTorrent client. In particular, the piece selection policies are implemented in the BitTorrent Transmission client, and results are reported for experiments conducted using the instrumented client on a controlled networking testbed. We have observed that the portion policy achieves a good tradeoff between playback startup delay performance and piece diversity.