El Clasicos

These are just matches that i've seen 10000 times. i don't watch enough of the other regions to know what is or isn't el clasico

Internationally

1. LLL vs OPTC. enough said. this is THE "El Clasico" cuz they always played internationally

Regionally in America:

1. 100T vs SEN. this one has been around longest i think

Regionally in Pacific

1. DRX vs PRX

Regionally in China:

1. EDG vs FPX

I can't think of anything for emea

emea is probably navi vs fnc(just based on 2 emea teams which performed amazing internationally)