I've decided I do not yet want to make our website be listed in DNS with an IPv6 address (AAAA record). Instead, the only way for now to access the site via IPv6 will be by an alternate name. The question here is which alternate name scheme is most preferred among these I have seen:

v6.example.com
ip6.example.com
ipv6.example.com
www6.example.com

Or do you have other suggestions for names that I have overlooked?

The matter of why I decided to not have both A record and AAAA record on our web site at this time is not the topic of this thread. Nor is the matter of why I decided to not just use all the names.

None are particularly intuitive, however to advertise and have it most memorable for users, I'd likely go the www6 route. That way if they do forget the 6 at least they'll land on your v4 website rather than get a server error.

Is there something that would be intuitive when one is motivated to find which hostname has the IPv6 address?

Another point. When visiting our site, visiting "www.example.com" gets a redirect to "example.com". That might complicate things. When if someone wants to be sure they are accessing via IPv6. Then "www6.example.com" should not do the redirect. This will then need another EV certificate since it is a separate name to end up at. Likewise, if someone has an issue where they need to end up at "www4.example.com" then there's yet another EV certificate needed (EV certificates do not come in wildcard versions).

Or maybe just not use EV certificates for the www4 and www6 names? We don't need an EV for hostnames that redirect to another name, so an ordinary wildcard certificate should do fine.

One IPv4 address for "example.com" with an EV certificate for "example.com"
One IPv4 address for "www.example.com" with a wildcard certificate that redirects to "example.com".
One IPv4 address for "www4.example.com" with MAYBE an EV certificate.
One IPv6 address for "example.com" with an EV certificate for "example.com"
One IPv6 address for "www.example.com" with a wildcard certificate that redirects to "example.com".
One IPv6 address for "www6.example.com" with MAYBE an EV certificate.

The www4 is for those who have issues once the main site switches to both v4 and v6. Some people are on networks or hosts that THINK v6 is available (host or network has v6 configured but v6 connectivity upstream is not there), and will prefer v6 over v4, and could see either a delayed connection (try v6 first, fall back to v4) or be unable to connect (rare cases won't fall back to v4 at all).

Once internet customers start to get v6-only connectivity (when v4 is really exhausted), then www6 will be for those that have the oppose problem as described for www4.

The main "example.com" site is v4 only for now, but will eventually be v4+v6 (maybe by end of year, maybe next year, depending on how access issues get cleared up, and numbers of people having them).