I loved Cloudtail and Brightheart so much. I loved how she was beautiful to him regardless of what she looked like and honestly it gives a lot of good lessons you could apply to the real world.
I loved all the classic pairings like Fire/Sand (how they developed was just so cute), Gray/Silver (though tbh I do prefer him with Millie now ^^' but I like both of the pairings pretty equally), and Fern/Dust definitely gets an honorable mention!
Second series I loved Squirrelflight and Brambleclaw, and I was so happy with the end result after everything that happened to them.
I really, really, really freaking loved Ice/Lion and it sorta sucks it all went a completely different direction and just never happened. :/
And finally I really love Jay/Briar. ^^