Since I consider mobile phones even less safe as desktop computers (especially as I use mostly Windows), I use mobile wallets only together with a hardware wallet.
This being said, although Green Wallet is open source and Mycelium is not, I do prefer the way Mycelium works and that's what I use on mobile. Again, this together with a hardware wallet.

If you want to risk and go without a hardware wallet, Electrum and Blue Wallet are very solid options.