which is possible (or both) heimdal or kerberos for heterogeneous network login
ie
unix kdc running MIT kerberos or heimdal clients (services) to kdc bsd/linux client (to authenticate to services examples authenticate or ssh) windows/bsd/linux
of come across a lot of text discussing this and at least for me it never gives a clear answer, what do I need to be thinking when making this decision?
Pick the Kerberos implmentation you understand better and have most of your clients implement. If you have more Windows machines, go with AD. If you have more Linux/BSD machines, go with MIT or Heimdal.
Answer from another question points to a good starting reference for Kerberos interop between Microsoft and MIT/Heimdal.
If you have Windows clients, you really should be setting up a domain controller, and use the Windows KDC. Then have all other clients (MIT kerberos and heimdal) authenticate against that.
If you don't need the domain functionality, it's also possible to login to a Unix KDC from Windows; there are Microsoft instructions on how to do that, but it's fairly tedious.
Heimdal and MIT kerberos should be completely interoperable for practical purposes, but I haven't tried myself. It's difficult to use them both on a single system, though.