I dunno how much has changed in the last decade, but Avid is an entirely different sort of beast as far as the way it expects you to set up your workflow goes. I find it works great if you’re the initial editor and are working from all the raw footage, but it’s difficult to work with from a fan editing perspective; Premiere and FCP are much more fanedit-friendly IMO.
I haven’t tried DaVinci though, so I can’t offer any advice on that one.
Avid is a pain, but it’s also the real deal. There are some under the hood aspects that it will always have an advantage with, but yeah… the others will be easier to use and better suited overal. The free version is designed to be quite a bit easier to use, though the media management aspects are likely to annoy people used to FCP7.
Resolve has some finicky media organisation in the app, and project files moving from machine to machine can be messy, but the editing functionality is very similar to Premiere and FCP7.
FCPX is still effectively in beta. They completely reinvented what they wanted an NLE to be, but there are still so many things it cannot do, not due to a lack of power but rather a lacking GUI. It also is more difficult to be as precise as quickly, due to the shared monitor and tracking with mouse hovers.
I’m an editor, I have used all of them many times for differing projects. Premiere is my favourite, but I use Avid most for work. The more media you have to handle, and the more you work with others, the better Avid is.