I'm really not sure. I also have the same kind of dilemma, Eth and Btc are my main investments and I'm sure in future's raise of both, but which one will bring the most of profit I really do not know, I just prefer to have them both in my investment portfolio.
Hard decision indeed, as most of us here knows that this two coins got their potentials and can bring good profits in returned, best to trust your judgement according to your understanding, if you will find some time to read more information about this two coins and see how progress delivered then it can give some good clues to decide whether splitting your investment or have some portions of btc being kept and invest more with ETH.