To start just get Fusion, it's not like your going to drop $6,000 to play around with Master-CAM. That was my quote last year on the mill 2D package. No maintenance. I own it. No lathe, no 3D stuff. I was all in at like $13k for all with training. You have to be making money to buy that.
If you are then lets get to my very loose overview. They both work well, the CAD part of Fusion is easier in my opinion. The CAM is much, much better in Master-CAM.
As for long term consider some things. I went back to a file I hadn't run in like a year. I made some changes and when I went to post they had changed everything. I spent hours trying to figure out where my stuff was. They even changed the posts so I had to re configure them. Not fun. More of an issue they had moved one of the toolpaths I used behind a pay wall. If I wanted to use it like it was I would need to cough up $1600 more a year. So at over $2k with the extra package (normal stuff you would want) I would in three years be paying what Master-CAM cost. For me that is a no brainer. Just need to get a small business loan to get all the packages and training I need at once. I do lathe and simultaneous 4th also.
Lastly if money isn't an issue here was the biggest difference for me. I spend honest to god hours fighting with Fusion. The functionality is there but it is never in a sensible place. It's one check box, hidden in one tab at the bottom with a weird name. If you know this, you are golden, if you don't your are going to go crazy trying to get simple things done. You just have to know everything, you will find nothing advanced by poking around.
With Master CAM things are much more intuitive. When I look in the place were it makes sense for something to be it's there. Vastly less annoying to use. No CAM is friendly but with Master-CAM I don't feel like it's fighting me. I do what would make sense and I works like you would expect. More work, less cursing and searching the internet for answers.
Just need to get a large lump of cash to get it all.