I use the following milters with Postfix:
ClamAV, OpenDKIM, OpenDMARC, Rspamd
This is also the order they are being called via smtpd_milters.
What would be the best order for them regarding performance, resources and spam protection?
OpenDKIM, OpenDMARC, Rspamd, ClamAV
I assume you have OpenDMARC configured to do SPF itself? You'll want to disable SPF/DKIM/DMARC checking in Rspamd then as well.