I should revisit again sometime soon and do new tests as I did leave things unfinished. I wasn't happy with the results for a 3D project I was testing and gave up for the time being.
Defold has SSAA built in. This is the samples option in the game.project file. Other methods have to be setup manually as post processing shaders - I can publish examples later, it would be handy to be able to be able to drop the different methods in/out quickly.
For 2D projects, these features are not really useful. For 3D projects they can be used to reduce things like jagged edges / aliasing. As Defold's 3D features improve, then they will be more relevant for more projects depending on the needs of an individual project. For now, it's not a topic worth too much time.
If you do have a 2D game with jagged edges for example when rotating an object make sure you add enough inner padding to the sprites. If your image has image data near the edges of the image container then it's more likely those edges will look bad when rotating.
Generally super sampling is better but more costly. The other methods are optimized approximations meant for specific situations with pros/cons each.
AA features are generally not appropriate for mobile games as they are costly. Unless you know you are only targeting devices such as the newest iPads then it's safer to use. Defold doesn't allow you to control the samples at runtime yet.