The ipv4 and ipv6 proxy servers use different ip protocols. If 4 is our old, good friend, then 6 is new and actively developing. This means that you must choose a proxy server depending on the sites you intend to use them with and their registration type.
A notable difficulty in choosing is what you need to decide. What to use - private or separate servers. It's simple: if you plan to use the proxy rarely and only for surfing, then a public proxy will be enough. If you need a proxy for serious purposes and plan to actively use it, then it is recommended to give preference to a private server.
Another advantage of a private server is the ability to reserve one or more IP addresses for itself. And this is its most important difference from a public proxy, where several people can use one address. You can buy proxies at best-proxies.ru.
Private proxies can offer their clients dynamic and/or static IP addresses to work with. A dynamic address tends to change during a communication session, and when choosing a static IP6, the user will receive a whole set of fixed addresses. On a public server, these addresses will not be your personal property, other visitors will use them along with you, and, moreover, perhaps even at the same time as you. If you plan to access through a proxy on a network where the address can be blocked, then it is recommended to choose a dynamic IP. So you can periodically change your IP address, and thus bypass blocking and bans at the address.