don't have the tri bar but i have the cusco rear stb.... i like it... i don't know hom much more of a difference the other two bars would make probably a lil but you might have to lose your rear carpet.
i'm using a triangle bar. it stiffened up the rear and kept it flat during cornering. however i did find that my rear inside tends to lift more during hard cornering. I'm looking to get a rear sway bar next before I go and change the suspension
I am running this bar. On the stock suspension/wheels/tires you will not notice a difference over a solid 1-piece rear sway bar. However, once you start adding stiff coilovers, stick tires, sway bar, etc, it's effect will become more pronounced. You will be putting dramatically more stress on the stut towers when you take a corner, and this will help keep them from flexing. This will also be more noticable on an older car or one with a chassis that is not as naturally stiff as the EVO.