A key part of my enjoyment to any OT3 fic is that they really delve into what makes each of the characters tick, in addition to exploring the psychological side of the triad--moments of jealousy and moments or syngergy, which sides of the triangle are closer and which are further apart. My favorite nuTrek 0T3 is George/Pike/Winona. I love writing them because Pike is presented as Jim's mentor/father figure in the film, and wouldn't it be intriguing if the reason why Pike is so invested in him lies in the previous relationship he had with Jim's parents? It opens up a whole new avenue through which to read the interactions between Pike and Kirk onscreen.

In TOS, the OT3 I love is Kirk/Spock/Uhura, especially the stories by Spock Jones. They are wonderfully rich, and leverage those tiny moments of interpersonal chemistry see into some of the hottest fic I've ever had the fortune to read.

Also, just for the sake of reccing, I'd like to point to the Draws series by syredronning, which begins as a Pike/Kirk/McCoy OT3 and evolves from there. She goes into great detail about the dynamics of each of the sub-relationships as well as the triad as a whole, and on top of that, weaves in an amazing sub-plot.