Whatever CAD package you decide on, you need to look carefully at the licensing structure.
Fusion 360 is an Autodesk product, it will periodically need to phone home to mother and see if you are still allowed to use it. If you are using it regularly this will be no problem. If on the other hand you are like me, there are periods of heavy usage then maybe several weeks of no usage, Autodesk can and will disable your account due to inactivity. DAMHIK! Most of the "Free" software packages will do this if you don't check in often enough, and this now includes Designspark 3D.
Most "perpetual" licenses, even the paid licenses, will require you to check in with the head office - to be sure you're still on the nice list and not on the naughty list. I think ProgeCAD is one of the few software packages that doesn't do this, but it's a paid "perpetual" license. If I understand their licensing structure it works like this:
1) You buy the "perpetual" license, I think this is about $400USD - and they even allow you to install that license on up to two machines. AND it's yours - forever, truly a perpetual license.
2) You have the OPTION of purchasing an annual maintenance package, not sure what that cost is but at the time I was checking into the licensing it didn't seem unreasonable. This will give you each and every upgrade that comes along, provided you keep buying the annual package. If you opt NOT to do this, you still have a perpetual license, at what ever the revision level was when you purchased the license.
3) If, 1, 5, 10, or whatever revision levels later you decide you'd like to upgrade to get more/better features, you pay a one-time upgrade fee and you're upgraded to the latest revision. I think the upgrade fee is the same as the annual maintenance fee. You don't have to pay for each revision level, unlike some other software packages.