In random broadcasting, source packets that have to be broadcast to all the other nodes are generated at each node of a network or a parallel/distributed system at random instances. In this paper, we propose several priority-based routing schemes for random broadcasting in general product networks and vertex and edge symmetric networks. Our goal is to achieve the maximum possible load factor p \approx 1 and optimal average reception delay (e.g., 0(nd + {1 \over {1 - p}})) at the same time. Our routing schemes are the first and only approaches reported in the literature thus far that lead to optimal throughput and average delay in many important networks, such as n-ary d-cubes, hypercubes, generalized hypercubes, and star graphs.