Sokka liked his girls delicate. He liked porcelain skin and dainty steps. He liked girls who would take his hand when they stepped out of a boat or carriage. He liked feeling like he had to protect them. Sokka liked feeling like the man.
That was why he was so drawn to Yue. She spoke softly and had soft skin and she was dainty and she didn't know how to fight at all. He felt stronger near her. He felt like the warrior, and he had intended to bring her home meat one day. Because that's what warriors did.
But her delicateness was her downfall, and he soon realized that if she had been a stronger baby, she wouldn't be dead now. She could have lived.
Then he met Suki, and she was everything that Yue was not. She was strong (stronger than he was if he was honest with himself) and her hands had calluses and she spoke loudly. She did not need him to defend her. She would be fine on her own.
That was why Sokka wanted to be with her. Sure, she was nice, but when he was dating her, he didn't feel like he had to worry. She was capable of fighting off the evils Yue had not succeeding in fighting against.
Although there wasn't the spark between them that there had been between Sokka and Yue, there was a calmness. He had one less thing to worry about.