There are many input devices you can use to jump in Geometry Dash, all with unique pros and cons. This document is a comprehensive guide on the various input devices and methods of jumping, as well as moving left and right in platformer levels.

These input devices are good for "classic" levels where you only have one form of input.
(Platformer levels require more inputs than just jumping, meaning other forms of input are better suited for them.)

Mouse
You can jump by clicking with your left mouse button. Many players prefer this method because of how it feels in their hands, as well as hardware specifications such as the polling rate. The cons to this method are that it is much more difficult to spam at high clicks-per-second than with keyboard-like devices.

Up arrow
You can also jump by pressing the up arrow on your keyboard. Many players prefer the feel of this input, and a lot of top-level extreme demon slayers use the up arrow to have a higher clicks-per-second (or CPS) rate, which give them an advantage for spam-heavy levels.

Seyodevice
A seyodevice is a standalone device that is designed specifically to be a good input device for fast-paced rhythm games such as Osu and Geometry Dash. It has both high CPS rates and high polling rates, making it a great device for almost any GD player. You will have to decide whether it is worth it to buy the device or not, since you have to buy them with money like you would any other keyboard or mouse.

Space bar
You can also use the space bar on your keyboard to jump. There are a small handful of players that prefer the feel of this input method, but not many people use space bars in the community due to its clunky feel. A lot of people's keyboards are wobbly because they are so long that they tip slightly more in the direction you press them from, though not all keyboards are like that.

In platformer levels, you are able to move in more than one direction, with 3 separate inputs at your disposal. There are a few three-direction setups that can be useful for platformer mode.

Arrow keys
You can use the arrow keys to move left and right, as well as jump in platformer levels.
Up arrow - Jump
Left arrow - Move left
Right arrow - Move right

WASD
You can also use the WASD keys to move in platformer levels. WASD keys have a similar layout and feel to arrow keys, but many gamers prefer them over arrows due to their position on the keyboard.
W - Jump
A - Move left
D - Move right

Space bar (jumping only)
Space bar can be used in place of the up arrow or W key, as it allows you to jump.
Space bar - Jump

Controller
Platformer games in general tend to feel better on controllers, and Geometry Dash is no exception. The controller is often the best option for platformer mode. Do note that connecting a controller to the game will put button icons over every UI element to tell you what buttons correspond to what actions. These can often be annoying once you are used to the controls, but there are mods for the game that can remove them, with mod loaders such as Geode.
Joy stick - Move left/right
Primary buttons (also known as A and B on some controllers) - Jump