I stand by my first statement, the best rivalry is The Omega/LaF/Evo. Every set, whichever of these alliances is not in a war competes fiercely with any of the other two who also manages to netgain. Everyone else just competes to compete with Omega/LaF/Evo when we netgain. Some alliances are successful in throwing up competition on an inconsistent, but noteworthy basis. That being said, the three consistent and fierce top netgaining alliances are LaF, Evo, and Omega. I would also note that, in a pinch, all three alliances can throw up remarkable war efforts and all three certainly earn their right to netgain through occasional war and consistent diplomatic means.

Fighting is easy, netgaining consistently and well is harder.*

*Note, fighting well is hard, but fighting consistently is pretty easy. It's easy to find/create a war; it's harder to avoid wars.