Sephiroth and Cloud have a terrible rivalry. It's not even really that much of a rivalry. Cloud fights him for basically no reason.
Liquid and Solid are clones and Liquid kind of defines himself by his relation to how much better he is than his his "brother". The fact that Cloud vs Sephiroth is winning is exactly what I expected but also evokes a feeling of "jesus christ the people who visit this site are ****ing morons and this popularity contest is painfully obviously a popularity contest with a slightly different name".