I need help in deciding on a bonsai for my mom for this year's Mother's Day?

Since I'm such a romantic, I like the heart shaped one best. I'm also allergic to flowers. However, the four that you chose are beautiful & it should be what your mother likes best. I suggest getting the gardenia one, since that flower is her favorite. Gardenias were my mother-in-law's favorite flower. She was thrilled whenever she received them. It sounds like you are a very caring son. :)