Overleaf is a collaborative writing and publishing system designed to make the process of producing academic papers much quicker for both authors and publishers, from Writelatex Limited in London.
Overleaf is good to use in a lot of scenarios where something is to be written as a group. However, I believe that it is only good up to a certain amount of people working on the document at once. While I am unsure when it becomes too much, I got no doubt that there is a limit for when it is that good. Though normally, our group size of up to six people has been fine to work with in Overleaf.
I would recommend Vim in any scenario where text files have to be viewed, created, or edited on GNU/Linux computers. Regardless if you need to quickly change a few things in a configuration file, or you need to write up a full document, Vim is great. I wouldn't use Vim to view, edit, or create anything that requires "rich-text". In other words, if you need to format the text (bolding, font colours, word-art, etc), then Vim isn't the tool to use.
It's easy to use for a variety of skill levels. It has most features you could want from an text editor and LaTeX editor. Collaboration is easy for all skill levels including for first time users. The UI is pleasant enough and the website is quick to load. All the packages you need are available.
I don't consider the steep learning curve to be a hinderance on the overall usability. I would rate this a ten, but to be honest a lot of people do get hung up at the beginning and just abandon it. However, for people who have made the moderate effort to get over the hump, nothing can be more usable.
There is no commercial support for Vim. Thus, it will not get a mark beyond 5. However, community support is very good. You can easily find solutions for most of the problems in the community.
Alongside Overleaf, we have tried using Microsoft Word and Google Docs to write reports. While they all let you write in the same document at once, Overleaf just works better for us. Microsoft Word locks the paragraph someone else is working on to avoid others messing with it before the original writer is done. However, it is often slow to open those paragraphs up for others to edit. Google Docs is the hardest one of them to make a good layout on, though with the app, it can be good for proofreading on the go.
Vim's keybindings are a lot more complex than Notepad++. With that, comes a whole bunch of capability that Notepad++ just can't match. Emacs is comparable, in terms of capabilities--because Vim is built into so many unix systems, I chose to learn it instead of Emacs. Knowing both probably isn't a bad idea, but there's enough to learn in either camp to keep you busy
