That's an easy one. Everyone who has seen Young Sheldon must know that it's Paige.
Sheldon and Paige had great chemistry. Friendly, rivarly, teasing. They had similarities, they were also different. But perfect for each other. Sheldon did things for her that he didn't do for anyone else. The geeky and antisocial Sheldon, who disliked physical contact and never showed interest in anyone, had an affection for Paige. Paige also had no problem at all getting young Sheldon to kiss her (even if only as a prank).
I like Amy, but not as a partner for Sheldon. She was introduced as Sheldon's female version. There was no chemistry or affection between them. Sheldon hadn't shown interest in her for a long time. I found their relationship forced and a bit awkward. Amy was constantly forcing herself on him and running after him. On the other hand, the relationship and chemistry between Sheldon and Paige was natural, genuine and enjoyable.
