I voted 5th. At first level you're still excited about your new character, can't wait to roleplay him and a TPK puts a serious damper on your plans. By 5th level you've gotten used to the character, maybe bored with it, and you're coming in to those nice abilities. So at least then when a TPK happens and you redesign your character, you've got something meaty to work with, and you're not that attached to the character. By that time you'll also know if you liked the concept, so you might be hoping for a TPK. At later levels they're more likely to happen, sure, but then if you got that far you might really be attached to your character.
Pinotage