i keep a chamber flag in the chamber and a loaded mag inserted.
I'd strongly recommend NOT using a loaded mag with just the bolt "locked" back as a gentle smack of the butt on the deck can easily "unlock" the bolt and send it home, loading a round. the flag prevents this from happening.
Another option would be bolt in battery on an empty chamber with a loaded mag. I don't like this because the assumption is that when you need it, you'll pull the charging handle to load it and that introduces the opportunity for short-stroking it under stress, causing a malfunction. I have been advised by people who should know, and personally prefer to use bolt release to charge the weapon whenever possible.
another option is condition 1, ready to fire. This is probably the way to go for most people, but I am fairly constantly diddling with my rifle, so that would mean constantly chambering and then making it safe. I don't like chambering rounds in the AR indoors because of the remote possibility of slamfires. (I have witnessed several, even some that to the best of my knowledge were not ammo-related) If you do choose this option, be extra double careful about rule #2