Welcome to the 405th Terrabella. It's a hard comparison to make on which is easier between 3D printing and hand making armour (by that I assume you mean pepakura/foam), because it all comes down to what the individual is competent at. I'd say foam and pepakura are more "straightforward", as in you can get in and start right away. As you work you start to refine your skills over time with experience and different tools. 3D printing however requires you to learn a few things about how 3D models work, as well as some engineering/chemical properties of your printer and filament. Not rocket science, but can be a bit of a learning curve.
In the end, it boils down to personal preference. If you love working with your hands, making a part from scratch, foamsmithing or pepakura may be the way for you. If you're a bit more tech savy, or want more of a hands off approach for the construction of armour (it gets more hands-on when cleaning up and painting), 3D Printing might suit you better. Many of us even take the hybrid approach to our builds!
Compared to foam, printed parts will of course be more solid, but are prone to damaging in different ways. Whereas foam can be flexed, cut or torn, printed material can warp in the heat, or shatter if it lands with enough force (this depends on a large number of factors though, and there are ways to toughen it).