If you had 100k, you spent 50k buying BTC at 20k in Dec 2017 and felt like shit. Now is May 2018 and you have 50k left, which coin would you put your money in so that you don't feel the same way ?
If I was in this situation, I would have bought BTC when it went down to the range of 7 - 8k USD. This will help in averaging the purchase price of BTC. With rest of money, I will buy ETH.
I follow two rules while making an investment, never invest all in one single coin and always buy in chunks.