There is no question about it. After testing MainWP for several months, we are sticking with ManageWP for our professional WordPress management solution. Maybe it is the learning curve, but I highly doubt it. I just like the polish that comes with ManageWP over the raw bones approach of MainWP.
It is not that it doesn’t work, but it is just much easier to get a full overview of what needs my attention in ManageWP. Even with their forthcoming new design (titled Orion), which I will have to spend some hours to learn the nuances of, I still prefer the attention to detail and the overall simplicity. ManageWP makes it much easier to get an overview of my sites that need updates (or which plugins or themes need updates) from a macro view of 50+ website more efficiently than MainWP does for the 5 that I was testing.
So what is the #1 reason that I am going to continue to use ManageWP? Efficiency and simplicity of the interface. I can get more work completed faster and that is the most important distinguishing factor between the two programs.
Feel free to take ManageWP for a test drive and use my affiliate link. I do not recommend software that I do not believe in.