The GP2040 firmware is extremely popular for its low latency, decent compatibility, SOCD cleaning, and more—especially if we’re talking about the GP2040-CE variant.
The FightBox M8 is a metallic & acrylic hitstick that comes with Sanwa and Baolian buttons as well as a Sanwa joystick.
The Mavercade Lightweight is the Floyd Mayweather of controllers: its low profile buttons allow you to pull off combos at lightning speed!
JumpHack is one of Japan's finest sources of highly customizable controllers, such as the JumpHack11-XL (also known as the JH11XL).
The Studio is so customizable that—in addition to its layout—you can pick the colors of its buttons' rims.
Ultra Arcade's Standard series is a reasonable entry point into its customizable controllers, and there are Pro & Lite editions available.
The Mixbox comes in variations from all-keys to southpaw, but you may be most interested in its S+ variant that has 13 buttons and a spacebar.