Passive optical networks (PON) promise to open the last mile bottleneck in next generation access networks, permitting the transport of higher data rates than conventional copper and copper-fiber hybrid technologies. As a result, several PONs architectures have been proposed and among those, the two prevalent architectures are: one based on time division multiplexing with a single wavelength optical channel on each direction, and the other based on multiple optical channels using wavelength division multiplexing technology. This paper provides a critical and comprehensive comparison between the two. Through the use of simulation we will highlight their differences in terms of scalability, performance and access distance.