The search for good stories about those two always leads me back to Archive of Our Own. Their tag system is really thorough, so you can filter for the pairing and then sort by kudos or bookmarks. That usually surfaces the most popular works. I sometimes cross-check on fanfiction.net out of habit, but the tagging there is a mess for something this specific, and the quality is way more hit-or-miss. The good stuff tends to migrate to AO3 anyway.
What's tricky is that 'top-ranked' can mean different things. A story with thousands of kudos might be a fun, tropey one-shot that lots of people enjoyed, while a slower, more introspective character study might have a smaller but more dedicated following. I usually look at the comments, too. If readers are analyzing the themes and writing thoughtful essays in the comments, that's often a better sign of a deeply rewarding story than just the kudos count alone. My favorite one for this pairing is probably 'Rex Lapis Takes a Vacation,' which is just a wonderfully quiet slice-of-life thing about responsibilities.