I use a solid box in a terminal and for coding, and a vertical bar for writing in emacs org-mode. But I recently tried out a one-third box[1] in emacs and I am really loving it! It's partway between a box and an underline. Some software has a half-box option but I don't think MacOS Terminal or iTerm2 have that. [Edit: I was wrong — iTerm2 has an advanced setting for "underline cursor width"]

I used to use flashing but have that turned off right now, for reasons I can't remember.

[1] (setq-local cursor-type '(hbar . 8))