First of all, you mention that you are using the Switch Dependent configuration / Hyper-V Port distribution policy. You might consider trying out the Switch dependent / Dynamic distribution policy, though. According to Microsoft's Windows Server 2012 R2 NIC Teaming (LBFO) Deployment and Management document, the latter is the first recommendation in all scenarios where a switch dependent deployment is desired.
[Switch dependent configuration / Dynamic distribution] mode is best used for teaming in all cases where Switch Dependent
configurations are required by policy. Depending on the capabilities
of the adjacent switch it may also do very well, and perhaps even
best, when supporting teaming of native workloads.
In all cases where [Switch dependent configuration / Hyper-V Port distribution] configuration was recommended in Windows
Server 2012, the new configuration, Switch Dependent/Dynamic, described
in 3.4.6, will provide better performance.
Anyway, on to answer your actual question, the benefit of using Microsoft's built-in teaming capability is that your NIC teaming issues will now be supported by Microsoft (to a much greater extent than if you were not using Microsoft's NIC teaming.) Whereas if you use Broadcom's NIC teaming software, Microsoft may tell you to go bark up Broadcom's tree in case of a support issue with your NIC team. On the other hand, Broadcom's drivers (and NIC teaming software) may very well provide better performance and/or reliability with your specific hardware... because those drivers were designed for that specific hardware. So that is the major pro vs. con that you'll just have to weigh for yourself.