Haha that’s a tough question, there are so many of them that are so amazing.
I’d choose Aerith. (But I considered Tina, Rinoa, and Yuna. And I think I’d fall in love with Tifa it’d be hard to think of her as ‘just’ a friend haha, or else normally I’d say her.)
A Promise to Tifa, Etched in his Memory.
When Cloud left the village dreaming of being a SOLDIER, he swore to Tifa that he would come running to her rescue if she was in trouble. While it was Tifa who strong-armed him into making the promise, it seems that the idea that he must keep this vow was forever in Cloud’s mind. In BC he is obsessive about protecting people, and if he runs out of strength part way though he will mention the “promise.”
FFVII 10th Anniversary Ultimania Cloud Strife Profile p36-41
Tifa meets with Cloud at the Water Tower he had called her out to. She received the promise that he would “save her when she was in a pinch” from Cloud, who had said that he wanted to become a SOLDIER. FFVII 10th Anniversary Ultimania Complete Timeline