What contract management system is better for multiparty negotiation?

There are a lot of them but i would recommend you to try Contractlogix (it is not very popular but still), Parley Pro, or Concord (but the last one is better for large businesses). If I'm not mistaken you can find a live editing function, redlining and built-in e-signature function in every of them. So its up to you to try and decide which one is better fot your particular needs.