It shouldn't be that hard to remember: if you're specifying a numeric node ID, use id. As in the URL: /?node_id=43037. Node IDs are numeric. Otherwise, it's like giving the title of a node, as in the URL: /?node=What shortcuts can I use for linking to other information? If you ever pay attention to URLs, it should be fairly clear that node_id= is used when the criterion is a numeric node ID, and that node= is used when searching by title. But perhaps more to the point is that node:// is not documented and not supported, so no one should ever use it. Even so, some people have really got it in their heads. I'm looking at you, kennethk, Bloodnok, TGI, repellent, broomduster, pc88mxer, apl, oko1, pileofrogs, Herkum... ;-)

I always know that only one is correct, but I keep misremembering which one it is.

Um... Writeup Formatting Tips is prominently linked below each post form textarea, and that in turn links to What shortcuts can I use for linking to other information?. If that's not convenient enough, you could drop a link to What shortcuts can I use for linking to other information? in your Personal Nodelet or whatever.

I see you've discussed this topic in the past...