[inter-note: My use of the term shape covers exactly how it sounds, the shape of the overall d-pad, not exactly the mechanism of it as I tend to treat that as a secondary matter all together.]
As time goes on, the list of my preferred benchmark games changes because new games come out and do a better job than a game that was previously on my hitlist. Every game on my list provides the opportunity for frame perfect execution of certain techniques without fail in order to test the adaptability of my thumb to the shape and that each game does their job of highlighting key platformer marks required to get the feel of a d-pad for myself.
[inter-note: Questions to ask yourself when experimenting with a new shape:
•How many times can you execute that technique on that level consecutively without fail compared to previous attempts?
•How well is your muscle memory adapting to techniques you've had down to the dial in the past?
•[for those that have never had calluses] Do you already expect calluses from the long term use of this shape?
While not genre defining at all, Super Meat Boy represents platforming in it's rawest form which is why it's the very first game that comes to mind every time I encounter a new D-pad out in the wild. It will most definitely teach you to appreciate how far the horizontal flexibility of a good shape will get you in this game. The reason I stray away from fighting games for shape research is because of shit like Ryo's Zanretsuken which requires amazing horizontal precision and timing on a d-pad, specially in the middle of a match. On a fresh set of thumbs this constantly proves to be far too stressful but might otherwise make for a great horizontal flexibility test for people that use pads in fighting games.
Cuphead is a new entry in my benchmark army because it brings about many elements from different 2D genres, not just platforming, so simply being able to comfortably beat a boss or run 'n gun without stressing out my d-pad or thumbs is a huge plus. Hard to think of a game that can satisfy multiple needs that much at once so if you're looking for a reliabilty or versatility test then look no further than this recent gem right here. Another game you may want to experiment with for versatility is Duck Game due to it's heavy use of the d-pad for certain maneuvers where a great shape will give you an edge at your next couch gaming kickback.
One game that might rival Super Meat Boy in the horizontal flexibility department is Super House of Dead Ninjas but the reason it's one of my benchmarks is also because many actions outside of movement are tied to the D-pad much like the other two benchmarks sharing this category, Volgarr the Viking and Rivals of Aether. The D-pad is a tool there to assist you, not fight you so when it comes to execution of directional specific actions the shape will tell you right away how well it is willing to lend itself for that purpose.
For now this wraps up whatever this is. If anything comes up I may edit this or just follow up.