  In various multi-agent negotiation settings, a negotiator's utility depends,
either partially or fully, on the sum of negotiators' utilities (i.e., social
welfare). While the need for effective negotiating-agent designs that take into
account social welfare has been acknowledged in recent work, and even
established as a category in automated negotiating agent competitions, very few
designs have been proposed to date. In this paper, we present the design
principles and results of an extensive evaluation of agent HerbT+, a
negotiating agent aiming to maximize a linear tradeoff between individual and
social welfare. Our evaluation framework relies on the automated negotiating
agents competition (ANAC) and includes a thorough comparison of performance
with the top 15 agents submitted between 2015-2018 based on negotiations
involving 63 agents submitted to these competitions. We find that, except for a
few minor exceptions, when social-welfare plays a substantial role in the
agent's goal function, our agent outperforms all other tested designs.
