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...