Why put sys.aud$ to sysaux?

It’s not a secret, that if you leave sys.aud$ in system tablespace, you can catch high buffer busy waits because of freelist management of system tablespace.
But which tablespace choose for moving? SYSAUX or user tablespace.
One more point for SYSAUX from Data Pump:

When transporting a database over the network using full transportable
export, auditing cannot be enabled for tables stored in an
administrative tablespace (such as SYSTEM and SYSAUX) if the audit
trail information itself is stored in a user-defined tablespace