Ethereum has the most potential as a long term investment considering its rate of adoption is far greater than most competing platforms and new developments and updates to this platform will increase its marketshare further and help it to achieve more potential value in the near future
It is even wrong to pair both coin for comparison because they dont have the same function and project line, and moreover, Ethereum has been in the game for long and they have been able to satisfy all their existing and potential users. Ethereum still therefore remain worthy to be relied on for long term investment, but BAT too is not too much bad of a coin to hold.
In BAT space, they are functioning perfectly well, and they have also been able to develop their platform to the fullest. If I were the op, I would not compare both coin, I would rather plan to invest on the two coins for the future, while whatever question I would ask about the two would be the percentage of what my investment should be in both, which I would say should be 70:30, 70 for Ethereum and 40 for BAT.