It will depend on what you need and want with toning RC papers. We have tested a few and as I remember Berggers RC in selenium had a very nice warm brown tone, Seagull will also make a strong color shift. Have also toned Ilford's RC in sepia and then in selenium and ended up with chololate.
ALso, have used copper and iron , separtely and split with success. Of course these last two are not archival but RC is still toning.

In fact as i am typing and thinking. In our toning class which covers the basic toners at least one or two people tossed in some RC with results.