What is the safest way to log MEW among of these?
1.Keystone File
2.Private Key
3.Connecting Metamask.
Whatever key you are using is it really need for you to be careful enough not to misplace and put your key on somewhere else. Never give it to anyone as it is your life. All the coins you have invested are all there. You have to be careful at all times as there are scammers everywhere.