Its called a gate, and the most commonly used is the Square gate that it comes with. Not just because all Sanwa’s come with that as their default, but because its widely considered by the majority to be the best.
You sound like a beginner to japanese sticks, i say try to give it a chance and play on it like that a little everyday for a month. Then see if you still don’t like it.
The Sanwa JLF is still a fine stick, no need to replace it completely. There are other gates you can easily change it out with that will change the feel of the stick, like the Octo gate with a more rounded feel to the “U.S” style.
Square on left, ‘rounded’ Octo gate on right
Edit: as far as the buttons go don’t bother, it sounds like your biggest issue lies with the stick. Unless you don’t like the colors.