1: ConAi is a more mature couple
2: they have more in common
3: they look better together
4: Ai is able to help Conan, Ran only becomes a burden
5: Ai can take care of herself, and doesn't need constant protection, while ran freaks about little things and is always hiding behind conan's back
6: The two share a closer relationship
7: Even tho ran and shinichi known each other longer, Ai knows and understands conan better
8: Even if Conan was to get in a dangerous situation, she believes that he will be able to get out of it, and is able to offer intellectual help when needed
9: Shinichi and Ran's personalities clash, while Ai and Conan's fit more together in the whole scheme of things.
10: No matter how much ran may like shinichi, the only one he can really depend on as conan are those who know who he is, and the only one possible as a match for him, for then and the future, knowing who he was as conan and as shinichi, would be Ai
11: Dude, admit it, they are just right for each other, the girly personality of ran does not suit Shinichi's, even tho the damsel and the knight are often used... i don't see it working out that well in this case... i just don't know how too12. Ai never really forces Conan. She always gives him choices. But Ran, she forces Conan and even her dad(how rude) to go to the museum. I agree all this.