Dead.
For many reasons.
1. It's cheaper.
2. It's convient. i.e. no need to feed and house the mouse.
3. It's safer for the snake if it doesn't feel like eating.
4. It's safer for the snake even if it does want to eat it.
5. There is no real need to feed a captive snake live food. It doesn't work like that.
6. It's less distressing for the snake.
7. It's less distressing for me.
8. Sending a live mouse to the sloughter is cruel. Even if it is to feed your treasured snake.
9. They can be buyed in bulk.
10. They're easily stored in the freezer till needed so have no life span.
11. You can readily choose your size of mouse for the snake your feeding.
...need I go on?