I gotta say Pantheon and Leona. IMO it would make the most interesting couple since there is already so much going on here and we have few details on Pantheon and Rakkor overall.

They were childhood friends, trained and studied together.

When Leona would not execute her enemy during the judgement the judge called for Pantheon to convince her to do it, obviously because they had a thing and Pantheon would have some influence over Leona (Possibly).

Pantheon was super shocked when it turned she was the chosen of the sun, you would think that a Rakkor (especially the PARAGON of the Rakkor) would simply forget about someone who he/she might never see again and simply not care, though it could be that Pantheon never really could forget about her.

And then there is the Diana thing which might shake the Rakkors faith in the Solari, therefore shake Pantheons faith in Leona.

I would root for these two.

Garen and Darius <3

I just want to see Riot release a champion that Rammus could love. He seems so lonely to me xD

Can't believe that no one has suggested Skarner and Taric. They both miss their homes, and, of course, Taric thinks that Skarner is truly outrageous.

my number one league otp is garen x kat, but right now i'd have to say
sona x lee.
lee is blind, sona cant talk. running around aimlessly.
awwww yeah.