What will be the second biggest cryptocurrency after Bitcoin in 2019?
I think you should have clarified biggest in terms of what ?
If you see the market data, then based on market cap , XRP is already in the second position and fetching a lot of attention from legit entities as well. However, Ethereum is not too far from it. I think, Ethereum is going to beat XRP because I see more and more dapps being built on it.
Again all these are my personal opinions :)