Migrate Kentico 8 to 13

There are several ways we've done it but it's based on the customer and their install. The structure of a user, customer and order have changed significantly 7 versions.

I'd ask yourself what data are you willing to not migrate or lose. If the answer is none, that's fine, it will take you longer to do you migration. Secondly, I'd use the Kentico Import Toolkit as much as you can. Use the API as much as possible and script other data with SQL as a last resort.

Upgrade them all the way to KX12 portal engine, then use the Kentico 12 Portal to 13 converter.

Definitely should ask the question of if it's needed/worth it, and what is being preserved. If they have a ton of content then usually this is still the fastest route, but if they don't have a ton of content and/or it's easy enough to rebuild from scratch, probably better that way.

We've already upgraded 2 portal sites to KX13 using the converter and in the processes of converting 2 more. The converter can preserve all your content, including migrate widget content, but in all of our cases the sites had a ton of content that starting fresh wasn't an option. hit me up if you need help.