it is depend on situation. when i use for browsing (read only) i prefer mouse only. when i use for playing video, keyboard is my choice.
Why ?
When browsing i prefer reading mostly than reply. except in this board
When watching video, i can control fast forward, backward, pause, play and many control using keyboard.
Both of course is the best answer. Only one is missing, there will be difficulty to use the computer.
Without keyboard, then that will lost of typing and input characters and symbols and very hard to use the computer or even the computer will not be use.
Without mouse, then that will burden to navigate the interface such as buttons, directories, surf internet and others.
I prefer mouse. You can still use a computer without a keyboard, it's called a laptop, it has built in keyboard. I generally prefer laptops over desktops because I can move anywhere and get things done faster.
Since I am into posting, I use the keyboard a lot than the mouse. But there are times when I do some designs in the computer and in these times, I use the mouse more often than the keyboard.
Keyboard. As screen realstate increases, mouse gets slower. Get a nice mechanical keyboard, take some time to learn the keybindings and just watch the magic happen. Awesome WM, vi, vifm, and Firefox with Vimperator are my weapons of choice. Also, it hurts my hand a lot less.
I prefer to use both of them, I dont think i ll make it good usage of computer if mouse or keyboard is non functional. so both are equally good to use for me.