Hi,
I have solid experience in implementing documentation tools and systems for small and big companies from the USA, UK, France, Germany, Switzerland, Denmark, Spain, I also created a lot of user guides for my customers, so let's discuss more your project.
Based on your project I already have a few questions which can identify what tool will suit you the best:
1. Do you have limitations in your budget when it comes to a new documentation tool? Different tools cost different based on your needs, how many users you have, etc.
2. Do you need a documentation tool just for the user guide or also for other needs? For instance, knowledge base, technical & business documentation store, etc.
3. Do you need any features which allow you to restrict user access?