I'd strongly recommend using Illustrator over Photoshop for motion graphics, if you're gonna stay in the Adobe family.
For one, you can then use "Create shapes from vector layer", and super easily do path animation and more fine-grained and complex manipulation within after effects (see: https://medium.com/bridge-collection/adding-a-little-motion-to-your-portfolio-7f1afae9bec5, and http://www.sternfx.com/tutorials/114).
For another, you preserve fidelity while transforming layers, especially when scaling.
It's also just much less setup on the pipeline end, and more tolerant of deciding to make changes with how the animation is composed later on.
Also, for those intimidated by After Effects, see again (https://medium.com/bridge-collection/adding-a-little-motion-to-your-portfolio-7f1afae9bec5). It's a great step by step walkthrough of an example motion graphics pipeline within AE, that assumes no preexisting knowledge about the software.
This is a very good point. For a project where we want to preserve scalability at all sizes, like a brand identity, and then we would start the toolchain in Illustrator.
Where we (and Molly) have found Photoshop to be advantageous is its incredibly broad rendering capability. It has great path and vector tools, so there's no issue with creating elements that scale well. But, it also has tremendously deep and sophisticated tools for typography, blending, transformation, and raster pixel manipulation. This toolchain can be incredibly helpful when you are designing an interface that may make use of an advanced, or altogether new, graphics library.
One of the experiences we've had recently was working on a gaming console. Many of the newer tools for design or animation didn't have the ability to preview what could be done on the platform we were designing for. After Effects, in particular, also offered some programmatic motion capabilities that were very important to solving some questions in the brief.
We also had another good learning experience designing an entertainment app that, among other things, could re-composite camera video on the fly. In this project, it also made more sense to use Photoshop to think through the interface and camera content in tandem. Again, an unsolved problem that required the use of a non-standard graphics library, and PS & AE made great tools at the earliest stage.
All this is not to say we do not use Illustrator, Sketch, Origami, Principle, and other tools heavily. We do, but our studio always takes the position that ideas come before tools. So, as you pointed out, there are absolutely times when Illustrator is a better tool for the job.
In the future, I think we'll probably write an article about our experience and perspective on tools as a whole and how they relate to design—not just for drafting an interface, but for all around creative problem solving.
Every time, when I use AE for motion, I want to change a frame to millisecond exactly for Android.
I think I gulped when I saw After Effects was involved.
Yeah.. "Setting up your Photoshop File".
Do you guys have any constructive feedback or... ?
Everyone has varying toolkits depending on the project or the team. I use AE for motion design all the time.
Not a diss from me, I just thought the software looks very intimidating.
Gonna blow your mind but most folks still use AE for micro-animations :D https://code.facebook.com/posts/354469174916519/keyframes-delivering-scalable-high-quality-animations-to-mobile-clients/