This is a decision you need to make for yourself, weighing up the issues
discussed below.
Both accounts have the same issues: reliability, security and privacy. But the
university’s account has these issues with both the university and the service
provider (Microsoft).
On one hand, if the notes are an important part of your course, you might want
to use resources provided by the university for those notes. That way, if those
resources fail for any reason, you have an organisation to hold responsible.
Generally, with a free personal account, the service provider is under no
obligation to continue providing the service (at least beyond whatever notice
period their terms of use specify), so you do not have such reliability. Of
course, a paid personal account is a different matter.
On the other hand, if you do not intend for the university to see these notes
(which seems to be the case, based on your question), then you might want to
keep them off university systems. This avoids any issues with your privacy,
other people’s privacy, and any other legal rights that might apply (such as
copyright). In particular, it helps to prevent the notes from being used
against you in any dispute with the university, an issue mentioned by other
users.
You would still have the privacy issues with the service provider, but you
could deal with those by locally encrypting the data before uploading it.
This might not be an option for OneNote, but if you can make it work, then
there should be no problems. This is true for a university account too, except
that they might object to your use of encryption.
Another issue is that the notes are not just part of your course, but also your
writing that you should be able to use for whatever purpose you like. For this
purpose, you want to ensure reliable personal access to those notes, which
suggests that you should either:
- ensure that the university account has an effective export mechanism (that
you are disciplined enough to use when necessary); or
- use your personal account to begin with (but note that if it it is a free
account, it still might not be reliable, as discussed above).