I agree with vblanco, DDO is the lazy way of doing it, at least the older version (I haven’t tried the quixel suite one yet) isn’t going to give you your own style, all your stuff will have pretty much the same look as others that use it. Substance Designer have a lot more power and lets you create essentially anything you want, but you’ll have to create your own presets, which gives you much more freedom than making presets in DDO.
(NDO on the other hand is great.)
Also Subastance Designer is not a material editor, it’s more a node-based texture generator that produces textures to be used in materials/shaders.
Both are texturing softwares that generates your textures using presets rather than lets you “paint” them (although you can of course do that as well).
I’d say Substance Painter is going to be a better approach if you prefer to have more control and “paint” your textures, so if that would be interesting I’d say pick up Substance Designer since you can use substances made with designer inside of Painter.