It’s a tossup. MediaTek has improved after the launch of Helio P60, which is powering some of the devices. The MediaTek Helio P60 is combined blowing energy of four major ArmCortex-A73 processors among its centers.
However, Qualcomm Snapdragon devices possess better battery optimization than Mediatek, whose devices often have a short shelf life. MediaTek does not usually release its SoC source code to the general public. Between the two companies, both have created formidable products, so it is a race that ends with a tie, somewhat.
However, some would say that Qualcomm is substantially better because they demonstrate that because of its great battery life, it can have devices run all day long, and it charges very quickly as well.