I'd go with the fullsize personally. I know the Impala at least has a very large trunk. We used it last summer for 5 people with one suitcase each (3 of the suitcases were mid sized, two large),and a few grocery bags. It all fit!
We had to play tetris to get all our luggage in the back of my 2003 Accord to get to the airport. When I loaded up the Imapala in Flordia, I thought we had lost a couple of suitcases. HUGE trunk.