We have five proxy formats, and they differ not so much in speed as in the origin of the address and how this address appears to the site. Below is how IPv4 differs from each of them.
IPv4 and ISP
Both formats are static and equally fast. The difference is in the origin of the address: IPv4 belongs to a data center, while ISP is issued by an internet provider and appears to the site as home. IPv4 is cheaper and suitable for most tasks; ISP is used when IPv4 faces checks. The free 100% Uptime option is available for both formats.
IPv4 and IPv6
Both belong to a data center, but there are many more IPv6 addresses, and they are significantly cheaper. The limitation of IPv6 is one but significant: it only works with sites that support this standard — and not all do. IPv4 is compatible with all resources.
IPv4 and Mobile
Mobile is an address from a mobile operator, which is much more trusted, and the IP can be changed by link or timer. But it is more expensive, and the address does not remain constant. IPv4 is chosen when a constant address and high speed for less money are needed.
IPv4 and Residential
Residential are addresses of real users: rotation from a shared pool of more than 20 million addresses, payment for traffic, not for the address. They are used when a wide coverage across countries and cities and constant IP change are needed. With IPv4, it's the opposite: one constant address, and traffic does not affect the cost.
Short selection rule
Need a constant fast address and low price — IPv4. Need more trust with the same constancy — ISP. Need volume cheaper — IPv6. Need address change — Mobile or Residential.