Open source applications are available to students free of charge and can be accessed from any Internet connection. Some of the open sources prefer that you join or become a member.  There are some drawbacks with open source applications such as having to put up with advertisements. It is a good option for those wanting to save money and who might have strong computer skills

On the other hand, commercial sources offer more support due to the fact that is has a larger infrastructure with the benefit of an IT team.  There is a cost involved but it offers a wider variety of applications.  The expense can be a drawback for many students. Adobe Connect is the preferred source of GVS and from the comments of those teachers using it, it sounds like it provides an excellent synchronous learning experience.   

Basically I think you have to weigh the cost with the functionality of the software.  The commercial sources have more funds to develop the software and the open sources always seem to ask you to upgrade to a premium version.