Vehicular networks have brought the opportunity for new applications to improve the safety and driving experiences. With the help of VANETs, data can be disseminated among vehicles to transfer important data, such as collision warnings. Conventionally, structure based topology like R-Tree is used for stationary networks like wireless sensor networks. However, recent research shown that the additional overhead of structure based topology is unaffordable in VANETs. Therefore, structure free approaches must be used instead. In this paper, we perform an extensive experimental study to compare the two approaches in VANETs topology management using simulation. Our interests of metrics include the network performance, the mobility affection and the overhead of the protocols. The experiment results with these algorithms reveal a number of interesting insights. The results are analyzed in detail and their suitable cases are explained. Finally, we conclude the paper with some potential future works.