> 1) I upgrade from 17->18->19->20->21 and hope nothing breaks!
I've done this since about version 11. And I usually only get around to upgrading every few versions so it's been like... 11->12->13->14, 14->15->16, 16->17->18->19.
I do each upgrade one by one. Upgrade, login, check system status and resolve any additional steps it suggests (e.g., adding indices/columns, etc) then jump right into the next upgrade.
I've never had one fail on me. Even doing 3-4 major versions at a time it's usually less than a half hour problem.
I've done this since about version 11. And I usually only get around to upgrading every few versions so it's been like... 11->12->13->14, 14->15->16, 16->17->18->19.
I do each upgrade one by one. Upgrade, login, check system status and resolve any additional steps it suggests (e.g., adding indices/columns, etc) then jump right into the next upgrade.
I've never had one fail on me. Even doing 3-4 major versions at a time it's usually less than a half hour problem.