I myself prefer to scroll with the keyboard in tmux, but for moving the cursor and selecting text, tmux has a very, very long way to go before being optimally efficient and useful in this regard.

The kings of keyboard-based cursor movement and text selection are vim and emacs, both of which have a very rich and powerful toolbox of techniques and plugins that help the user do that quickly and efficiently.

For example, emacs has plugins like ace-jump-mode which lets you jump the cursor to any precise position on the screen by typing just one or two keystrokes. vim has similar plugins, like easy-motion and precisejump.

vim and emacs also have quick ways to select words, sentences, paragraphs, functions, lines, logical and visual blocks, the entire document, etc. This includes having full access to rich and powerful regex text matching, which can be used for selection.

In contrast to emacs and vim, when I try to move my cursor and select text in tmux, I feel crippled. So sometimes I do succumb to the temptation of using the mouse to select text in tmux, despite being quite comfortable and satisfied in using the keyboard exclusively in vim and emacs.