The NGP for me the line up and price will be the major factor to whether it's a first day buy of waiting till a price cut
From Sony: I would like to see from new gameplay/footage of Uncharted 3, Resistance 3, Final Fantasy XIII VS. Maybe since God of war 4 is somewhat confirmed maybe a teaser trailer to start the hype,I would like to some enticing move game that will make my buy one. maybe since valve is throwing some support to Sony maybe we'll see L4D 3 on the PS3
From Microsoft: just show me some gears 3 and I'll be happy, but I would to see some more 1st party exclusives(or just more exclusives overall) on the floor(last years E3 was pretty damn boring...after they showed Gears 3 and Reach) maybe make the internet explode and take another "supposed" PS3 exclusive.
From Nintendo: the "Wii 2" has gotten my attention, maybe some more 3DS annoucements; mostly pertaining to the line up(a Pokemon for the 3DS and a Golden Sun would make my day)