As much as I love 882, I think 217 might have more tales about it, but I could get behind either of them.
Now, I'm admittedly not terribly familiar with fandom, so my nominations are going to be primarily based on what important aspects of the Foundation I think they showcase. These are the articles that I would show a newbie to illustrate the corners of the canvas we're working in when we add a new article to the painting.
SCP-507 "Reluctant Dimension Hopper" is one that's important enough to me, at least, that I listed it as a meter stick on par with Able in my humanoids guide. It was posted to the wiki on 3 Oct 2008 by an anon, is currently at +202, and it represents the Foundation at its most compassionate.
On the other side of the coin, though, I want to nominate SCP-231 "Special Personnel Requirements", posted to the wiki by Clef on 3 Oct 2008, and SCP-590 "He Feels Your Pain" posted by Bright on 4 Dec 2008. They're currently at +398 and +78 respectively. If SCP-507 represents the Foundation at its best, 231 and 590 are the Foundation at its absolute worst.
I know 590's rating is completely dwarfed by 231's, but I'm still nominating it because I feel it gives another, important take on it. The cruelty in 231 is unknowable, unfathomable, elaborate, and exploits redaction for shock value like [insert some really offensive metaphor here]. 590's cruelty is not just knowable and fathomable, but simple and painfully human. 590 is doesn't have any redaction beyond a blackboxed name and some blackboxed years, and is fairly short, but it doesn't need redaction and it doesn't need to be longer. Adding either redaction or length would hurt it more than help, and I think that actually teaches a more important lesson than 231 does. In fact, my nomination for 231 was an afterthought and I was originally just going to nominate 590.
(May add more. Still going through the list to see if there's any others that haven't been mentioned yet.)
