Ideally, you should keep as large a percentage as possible of your crypto assets in a wallet where only you control the private keys. Electrum for Android or desktops is one good option. For iOS, there's BlueWallet. If you have a large variety of different crypto assets that you need to store, there's Unstoppable wallet. If you have never used your own trustless wallet before, using a mobile app is probably safer than using a desktop app. An even safer option, which you should definitely consider if you have a lot of crypto assets, is to use a hardware wallet such as Trezor.