That's the ultimate question, and it is yet to be answered by Kishimoto. But you got it wrong. The yang chakra went to the Senju. and the yin chakra went to the Uchiha. Man, you got everything wrong in your description. The Senju inherited his body with a much higher concentration of Yang chakra. The Uchiha inherited the sage's eyes with a great concentration of pure Yin chakra.
Yin and Yang are basic Chakra types. it is believed that the rest of chakra forms are just a mixture of those two basic charka types. Susano and Ametaratsu are pure Yin manipulation chakra techniques. Wood element is pure yang chakra technique.
Anyhow, the younger son is better cuz he looks cool like radiator and he didn't produce a bunch of emo psychos.