clomid is MUCH better established for PCT. Nolva is better for gyno, however using an AI is better than using Nolva.
Nolva is effective when used to "prime" for hcg use.
some people find even low dose clomid intolerable, for those people nolva is a good option, however generally clomid is superior when it comes to HPGA restoration. Nolva may also be used to "prime" for clomid. Nolva first then clomid.
Nolva should generally not be used with progestins or after progestins (some people do without issue, in others it has caused/aggravated post cycle gyno- likely due to PgR upregulation)