Hey Devki,
Both the universities are very close to each other in terms of ranking
While, overall, ETH ranks higher, EPFL is known to be better for CS related subjects
But for EPFL, you should know French
So, if you don't, your answer is clear
If you do, you can go to the program page of each university, look at the professors
If a teacher's research area aligns with something you're interested in, voila
You have your decision
Reach out to me if you need further help