If it's a pure drop, definately load up at eNom, Snapnames, and Pool.
If it's a "pre drop", you'll want to go to the preferred partner registrar. Snapnames gets almost all the good ones (because they are get all of Network Solutions, Register.com, Moniker, and several other comany's pre-release names), but a few do go through eNom, TDNam (for GoDaddy and associates), and Namewinner (for Dotster) as well.
If it was a GoDaddy "pre drop", it will go through TDNam even if you backorder it. Doing so just tips people off to it (because it shows up with a bid) so, if it does go TDNam, you'd be better off waiting until less than a minute to go in the auction to make a bid.