More than IX/SoL and IX/RAGE?
If we're only looking at Earth2025 (which I guess we are, since SoL/SoF haven't fought once yet in EE), I would look at IX as well! They had some awesome rivalries; not sure if any were fought 7-times, though :p

I'm sorry, but SoF/SoL is NOT be the best rivalry of EE, compared to the many other ones that we've seen. Nothing against SoF and SoL, but you haven't been rivals since EE existed. I don't know why this thread exists in the form it does :p