Arguaging seems to be the best tone for any of the lizard races, since the Sakkra react to it especially well, even when the player is a Silicoid.
The 'gas bags' and fish seem to like state or reason, as well as the Humanoid's (at times).
Other than that I haven't been able to see any real pattern. I hope that every race doesn't have a 'perfect' tone because that will make diplomacy even more lifeless. Although Civ3 didn't have a tone and it was fine, it also offered more options on the diplomacy front.