If you never used Freenode, why would you? Libera is just good ol' Freenode minus its old trademark.
I used to use Freenode...
Use Libera if and only if you want to communicate with the people who used Freenode. (Actually, if you want to communicate with the people who currently use Libera; there are people who use Libera who never used IRC before, and a some old Freenode users who have followed their communities elsewhere.)
I think that both, freenode and libera will end up dead. I sure hope that Libera stops spamming soon though...