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 cknsistyun value overtime.

Search on Bitcoin and altcoin books/resources (here on the forum) and look into them, to understand more on how it works.

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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.