In my opinion (and many other people's opinion) feeding frozen-thawed is the best way to go.
There are some dangers in feeding live mice to snakes, in that the mouse will try to defend itself and can severely injure your snake....think missing eye or bleeding wound on your snake, and you'll forget about ever thinking about feeding it live mice.
If you do, for some reason, switch to live, never leave the live mouse in the snake's viv unattended.