because I don't understand how the cryptocurrency market works yet.
If you do not understand how it works, maybe you shouldn't be investing just yet. Improving your knowledge about it should be your main focus right now. What you would be looking at is how they both work and the fundamentals behind them, this would tell you which is likely to stay above water. You can also use previous chart as a reference to know which has been more consistent in value overtime.
Search on Bitcoin and altcoin books/resources (here on the forum) and look into them, to understand more on how it works.
Also, the most recommended software wallet to use on mobile or PC is electrum, and if you want to purchase higher amounts, look into hardware wallets.
Investing without understanding the crypto market is a mistake made by so many users and its result is only loss. People from outside think that crypto is buying at dip and selling when high, while in reality its difficult to assess whats DIP n whats high. Right now market is very high and its not the best time to buy coins that are on there ATH. DYOR, before you make any decision. Its just my personal opinion.