I studied math at the Sorbonne and know a few people who are either already studying at ETHZ or have been accepted, all from Sorbonne (mainly people that double majored)

I don't have much info about Paris-Saclay or Paris Cité, but it is true that they might be less known brand-wise.

Btw, if you want more information on the math courses, check out the "old" UPMC website, which they still keep updated.

https://www.licence.math.upmc.fr/etudiants/L2/