The top 5 candidates in terms of national polling, that is everyone except Ron Paul, Duncan Hunter, and Alan Keyes.
Why national polling? National polling is meaningless at this point. In addition, given this is a New Hampshire debate, wouldn't it make more sense to use New Hampshire polls?
If New Hampshire polls are used, the top five (in the RCP average) are: Romney, McCain, Giuliani, Huckabee and Paul.