Some additional comments/notes:
General...
- I think XLSForm is valuable to learn and important for both KoBo and ODK.
- Kobo Collect and ODK Collect are near identical for your data collectors (since KoBo Collect is ODK Collect).
- Good survey design is just as key, if not more so, than the software. As is leveraging the automated/facilitated survey logic and etc possible in a digital tool. As is a data analysis plan created before you collect your data.
- ODK is the core of the ecosystem and widely used in humanitarian, development, civic, environmental, health, etc.
- There are lots of opportunities to contribute to (and benefit from) the ODK community on the software, documentation, user support, futures roadmap, etc.
ODK...
- ODK Aggregate allows giving users different permissions but each instance is generally for a single organization or project.
- ODK Central is a modern sibling to Aggregate that is easier to install, easier to use, and more extensible with new features and functionality both directly in the software and with the use of our REST, OpenRosa, and OData programmatic APIs. It provides better use controls and permissions for user access and campaign administration.
- Central makes it easy to encrypt your forms and data.
- Aggregate is easier to setup than KoBo, and Central the easiest of the three. IMHO.
- AFAIK, there is no public instance of ODK servers for people to use, although there are sandboxes people can use to test: https://sandbox.aggregate.opendatakit.org/ & https://sandbox.central.opendatakit.org/
- There is the separate ODK Build for a graphic form builder. Forms can be written in Excel using XLSForm syntax.
KoBo...
- The server component of KoBoToolbox includes the ability to have multiple segregated accounts. It is designed in such a way that a single instance (e.g. https://kobo.humanitarianresponse.info/) can easily have multiple organizations using it.
- OCHA currently makes available two publicly-available instances of KoBoToolbox.
- Setting up and maintaining your own KoBo server is an involved process.
- There is a built-in graphic user form builder. But some number of users, myself included, just author forms in a spreadsheet using XLSForm syntax and these are compatible with both KoBo and ODK (and several other data collection tools).
- KoBo Collect is a re-skin of ODK Collect and besides the color and app icon is largely identical. (The only difference between the two is the name, the icon, the default settings, and time. That is, Kobo Collect is usually a few months behind ODK Collect.)