Use blockfolio. There are a number of similar apps. Most will sync with all major exchanges and automatically track everything, but I had issues with past transactions and end up just going the manual route. Since I only buy maybe once a week or so, and only hold 4 cryptocurrencies, this has worked well for me. If you Google "blockfolio Vs" you will get a feel for the alternatives and the differences between them. Some allow you to track your stocks as well, some are mobile only, some you can actually purchase coins through etc. There's not really a "best" one, and most will do what you need.
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