I've never run the MaxNC, but have heard the program included is not very good; you might have to switch to an alternate 3rd Party. I contacted them 3 different times and talked to some people there that could not even answer my questions.
The thing about Sherline is that they do not make their own CNC machines; they are manufactured by many different 3rd parties. Support might be a problem.
I own a Taig, and it has paid for itself at least twice. I had a problem with scaling changing the A as well as the XYZ; I contacted Kurt and he changed the program. Maybe not for me, but their support is excellent.
I'll admit I am biased as I have not run the other 2, but I also looked into them before deciding on the Taig. Perhaps some other users can help you with the other two.