Well, Padme was an extraordinarily intelligent woman. While she loved Anakin with her whole being, I'm sure that part of that included loving his volatile, unpredictable nature. She knew why he was like that, and loved him for it, but most of all... she understood that that was just part of Anakin. Obi-Wan, on the other hand, was the exact opposite of volatile and unpredictable. He was steadfast, good, and honorable. If she needed someone she knew would be trustworthy in all situations, Obi-Wan would be it. Anakin... she had to have know that, while she loved him, Anakin was not as steadfast and trustworthy all the time as Obi-Wan. EDIT: I just got the 100th post! A winner is me!