Hi,
I am looking for most secured exchange to transfer my BTC, ETH & LTC to earn some interest by funding it , Leaving coins in cold storage does not earn anything on it
It doesn't have to earn anything,the fact that it is safe from exchanges and the dropping prices is valuable in the long run.Why do you want to throw them on an exchange and allow it to lose their value by trading/selling.Of course it depends on which coins you're holding.
Can you suggest which exchange is more reliable & can be trusted to leave coin for long term in order to earn some interest
Go for an exchange that is located in your country.Even better if they have a physical office.Random exchanges on the internet are going to steal your money with excuses like KYC and other bullshit.