Arduino Mega/ATK and USB storage.

Hi all, my first time here.

I'm planning to buy an arduino for a sort of datalogging system.
I will use an LCD display plus SD storage and some sensors.
After a long reading over the net I think I'll be able to manage it using AVR studio and Visual Micro for arduino plugin.

But I also need to write data into an USB key.
Wich libraries do you suggest? It will be better to use Arduino Mega plus USB Host shield, or an arduino ADK?

If I've understood correctly, arduino ADK also has an Host Shield on it, connected to RX1 and TX1, am I right?

If someone could point me into the right direction I'll be very grateful.