They are better stat wise since it's easier to break limit them but in terms of actual usage, it will vary on what SR you have as R eidolons do nothing but attack with fairly weak elemental attack. SR eidolon attacks actually have effects which is where you can benefit more using them.

I have a Darkness (highest attack R eidolon) fully break limit'd but I stopped using her because the lack of utility despite having higher attack than most zero break limit SR's I do have. Though you'll most likely have all SSR event eidolons if you play long enough.