This is a very complex question, and it’s next to impossible to give a definite answer.
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 that 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.
However, since the code is very young and decentralized, it is prone to bugs that can be pretty detrimental when they occur on big transactions. Also, the main thing that gives Ether the advantage that it currently has, which is the fact that it's built on Ethereum, might be taken away from it if another, even more, user-friendly platforms occurs.
Ripple - Ripple, on the other hand, does introduce a significant change. It is used for fast money transactions and as such has a lot of appeal to major financial institutions. This is something that makes it somewhat more stable and less prone to fluctuations.
It is not a cryptocoin in a traditional sense since it is mostly used to back the money transfers. Also, it is way less decentralized since the company that made it owns over 60% of all coins.
So options are there. It is worth noting that it is a very common practice for people to not invest in a single currency, but to build portfolios of a few of them. Also, you can always exchange one currency for the other. As long as you compare the rates and make sure you’re getting the best deal, that shouldn’t be a problem.