"In rough estimate: The Adreno 305 by itself has about the same efficiency as Mali 400 in those models.
Note that the Adreno 305 although slower clock is a newer and more expensive chip by design. The Mali-400 is usually placed with cpu's up to 1.6ghz to help pick up pace where the cpu lacks for screen resolution. Newest models of tablets/phones use the Adreno series in most name brands because the CPU takes care of the work the GPU chipset doesn't need to process,
Some of it has to do with the speed of the CPU as well, bringing even a few more fps and possibilities of more triangles, etc and shading,
As an answer The Adreno 305 for no particular reason other than stability of graphics.
Which doesn't say much since there is still tiny little glitches nearly unseen. Depends on how long you'll use the device. For the next 2 years lets say, you'd be good on an Adreno305 for gaming."