which mobile app (andoid) is better?
My choice is Electrum wallet.
Creating a watch-only wallet with Electrum.
On mobile, you can create it like this.
Create wallet.
Import Bitcoin addresses or private keys (because you want to create a watch-only wallet, after this step, you will import your Bitcoin address).
Paste your Bitcoin address.
Create your wallet password.
Finish.
Wait for syncing and see your wallet balance (watch only).