If you were to buy the DRM JS 30's, buy it for its two extra buttons—as well as one touch opening from its bottom.
You can buy the PadBox GS preinstalled with a non-split or split D-pad, and it's good for fighting games & other genres.
We can rave on and on about the benefits of the MS1, but its selling point is its unique right thumb button placement.
It's mind boggling how a small controller like the open source SplitFox Pro packs a split layout with 18 buttons into its little frame!
The Starburst is a mini leverless controller with 15 buttons, and you can tilt it to more than one angle for the comfort of your wrists.
The Data Frog Y5A's unique offerings range from an optional wireless connection to 27 mm buttons that are hard to find elsewhere.
The RC-OF1 is a variant of the OFOF1 chassis design by Rana Labs, so it features charm holes in all four corners.
If you don't need 16 or more buttons: the VSLAB VSNOVA N14 is a fine option with chamfered acrylic, customizable art, and cool LED.