This is a very complex question, and it’s next to impossible to give a definite answer. The reason being all of these have their pros and cons and virtually no one can give you more than a speculation. Here are the main points about all of these currencies..
Bitcoin - even though it’s not the very first currency out there, it certainly is the most popular and successful as of now. The market cap is way above all the other ones. It is often referenced to as digital gold, sort of an asset that gained enough momentum that it will remain valuable for time to come.
Having said that, this does mean that the network is overloaded leading to major delays in transfers, it has many major governments trying to regulate (and often limit) its use, it became next to impossible to mine and the price of coins as well as the transaction fees are way up there, so much so that it hardly makes sense to invest if you don’t have rather hefty amounts to throw at it.
Ether - Made using Ethereum, this currency has seen more than impressive growth. As of the beginning of 2018 it successfully surpassed 4 digits USD value for a single coin. The main advantage is the use of Ethereum on the backend, which is now used by many others to build blockchain based decentralized applications. It is way easier to understand and learn than the code behind bitcoin. For this reason, Ethereum has relevancy like no other and is being used by many institutions for all sorts of things. Thank you..