KVM Network, which Network Driver is the best

I am using a VPS with the following config
- SolusVM
- CentOS 6.3

Currently i am experiencing network issues and cant even use any real time application like VOIP.
A single call takes only 160kbps on the server side and is really terrible.
Single call means only a single call on the network with no parallel call and download at all.

My Provider told me that it could be because of the network card driver which is realtek at the moment and change it to virtue to have it fixed.

if any one can help me to understand this then please do.
thanks in advance.