I want to say here that I have made the mistake of using a very flavorful and somewhat hoppy stout before in a chili. Do not make my mistake. Keep the booziness low and keep it malty if at all possible. Think plain stout or Irish stout, not Russian Imperial, milk stout or a bit booze bomb stout.
Guinness is plain, simple and easily available. Not Guinness Foreign Extra, just the normal stuff. You don’t really need much either, you’re just adding depth of flavor. For that same reason, I use the same exact thing when making shepherd’s pie.