I am a European researcher and I had my PhD in 2018. After two post-docs between Germany and Canada I am planning to apply for a Marie-Curie individual fellowship. The best choice for my research would be to choose the person that was my PhD advisor as supervisor, but I am not sure whether this could give a bad evaluation for my application. Did anyone have similar experiences?
It's not ideal, but also not necessarily the end of the world. A number of the evaluation criteria touch on gaining new skills, enhancing career prospects etc., and on what you can bring to the host lab.
This is easier to write if you are going somewhere new, but not so obvious if you're applying for somewhere you've been before. So you'll need to make a very clear case why going back to the previous supervisor is best for your development - what are you going to learn there that you didn't learn in your previous time in their lab? Bringing in new expertise somehow (e.g. new collaborators, secondments etc.) may help you mitigate this too. You'll also clearly need to articulate how you're beginning to act as an independent scientist, which is again trickier with a past supervisor.
But, if you can make a clear case addressing those issues with respect to the evaluation criteria, you may still be able to write a successful application.