Sitecore regular provides new releases for Sitecore Commerce and Upgrade Guides. As far as I can see, if you need to upgrade XC 9 Initial Release to the latest version, you need to upgrade Commerce Engine and Sitecore from version to version.

You can't skip migration to Update-2 (for example), if you want to migrate to Update-3. Of course, it will take a lot of time for upgrade environments and will affect project budget.

I think, that instead of upgrade better to choose another way and setup latest version from scratch and migrate content. Because only part which you need to take care - it's a content migration. After that you can just switch production to new servers.

My question is:

What is a good way to upgrade Sitecore Commerce to latest version, on your opinion?

Sitecore regularly provides new releases for Sitecore Commerce and Upgrade Guides. As far as I can see, if you need to upgrade XC 9 Initial Release to the latest version, you need to upgrade Commerce Engine and Sitecore from version to version.

You can't skip migration to Update-2 (for example) if you want to migrate to Update-3. Of course, it will take a lot of time to upgrade environments and will affect the project budget.

I think, that instead of upgrading step by step, it is better to choose another way and setup latest version from scratch and migrate content and possibly analytics data. Сontent migration will be the most time consuming, yet relatively simple. After that, you can just switch production to new servers.

My question is:

What is the best way to upgrade Sitecore Commerce to the latest version, in your opinion?

Bonus questions:

Are there any license limitations to run 2 Commerce instances simultaneously during an upgrade? Is there support for Commerce xDB data migration available in xDB migration Tool?