Same, I really enjoy the twist in SoC, and it's ultimately a fairly touching tale, with some incredibly impactful and memorable moments. But I just really enjoy the interactions between Ico and Yorda so much. You feel like you really struggled through something with her, while SoC is such a solitary experience (whiich has its merits for sure.)
But I think the ending of Ico is what makes it my favourite - (some spoilers here) the part where the tables have turned and Yorda has to save you from falling, but is forced to let go of your hand as her mother overtakes her, is so gut wrenching. Then you wake up far below the castle and make an epic climb into the Queen's chamber for one last amazing battle. Then the bittersweet feelings as ghost Yorda saves your life by pushing you away in the boat while remaining behind. And then the after credits sequence where he finds her on the beach - I just love it all. It's a great fairy tale ending and I love that.
Also, I just love Ico's voice. The way he says "Ompa!" when calling Yorda just sounds great lol.