Anna,
Since this is a popular topic, I will jump in as well.
I am a doc editor and have spent most of my career on an Avid.
Up until recently, I considered Avid the best choice for ling form doc.
I have always found it better than FCP, which I am sure many will disagree with but having cut on both I just liked Avid better.
I am currently starting my third long form doc in Premiere.
I do not think I will go back to Avid. Definitely, do not cut in FCP as some have already voiced. It has aged out.
and save FCPX for shorter projects I think- myself, I am just ignoring it.
Premiere is a pretty remarkable program, and I think after the past few films, I am not looking back.
As for version, I am working in both 2015 and 2017. I have had no real issues in 2017, for what it’s worth…
Good luck.
Doug O’Connor
Z Post