Of course bitcoin,because this coin more promising in the future,and choosen of many people in many countries worldwide. Investing in bitcoin today will be profitable if holding it for a couple of years.
Both options are good to invest but Bitcoin is the most famous source because Bitcoin is well known digital currency and every should want to move on the Bitcoin and there are lot of Branded companies start accepting Bitcoin. As we compare on etherium in terms of popularity and returns of profit bitcoin is much better but as for now etherium also has a potential to gain huge profit it depends on our strategies and learning about investment method