I'm investing in both but I usually keep 60% of my investment in BTC and rest are divided into ETH and ICO's. I believe minimizing the risk is always the best way to go. I learned that lesson when I was 13 (bankrupted millionaire family haha)
All in is kind of leap of faith for me. And I like breathing :) So minimizing risk while breathing is the best for me.
Investing in highly correlated assets is not diversification, I hope you realize that.
I'm doing both also. The ICO's I've joined look real good at the moment Thorncoin, Finecoin, etc. I will also be keeping bitcoin and ethereum. I sold all the other alt coins. Bth and eth will control everything.