Selene/Lillie is the best yuri ship in the series, and here's why.
Many ships are based on the characters having scenes together. Dawn/Cynthia, Hilda/Bianca, Rosa/Bianca. They're nice, but they're limited in the amount of interactions you can have with them. Once you've seen all the scenes, the only way to have the characters interact again is simply to rematch them, and it's going to be the same team every time so their rematch doesn't have a lot of replay value. Or in Rosa's case, you just get to talk to her instead. Nevertheless, while looking solely at cutscenes, there's no debate that Selene/Lillie get more scenes together than any other ship in the franchise. Alola is infamous for its cutscenes, more of which focus on Lillie talking with the player.
The Battle Facilities have infinite replayability thanks to their randomized teams and focus on getting long streaks. Since some ships get to interact together in Battle Facilities thanks to multi battles, they essentially have infinite interactions. Instead of these ships having only "yuri cutscenes", they also have "yuri gameplay". The main ships that benefit from this are Serena/Shauna and Selene/Lillie. It's really fun trying to match your team with the other girl and go on streaks together. You can see the Battle Facility as like a date.
Other ships simply do not have that advantage. Only Serena and Selene get to go in a Battle Facility with their main yuri ship, and I think Selene wins over Serena after that based on the amount of cutscenes Alola has. Gloria can participate in the Galarian Star Tournament with Marnie, but it's not a Battle Facility; you're always fighting the same limited number of teams, so it's not as replayable as a real Battle Facility.
Now don't get me wrong, I'm not saying I dislike those other ships. It's just that Selene/Lillie has the highest amount of "in-game yuri" both in cutscenes and gameplay.