10% bigger
This may be a pretty minor point in the grand scheme of things, but it's something that grinds my gears a little all the time. From third life on, PC Elves are taller than NPC humans, Halflings are as tall as some elves, and don't even get me started on Humans, half-Orcs and Warforged.
Aesthetically it's just wrong.
As far as gameplay goes I find it annoying if the character takes up too much space on the screen, scrolling out is only a partial solution since this affects camera movement, visibility and how hard or easy it is to target a particular enemy out of a bunch.
I'd like to suggest that the change in size be made optional. This way people who want to visually show that they've invested the time and effort to level up to 20 and beyond several times can do so, and those who prefer not to play a freakishly tall character can do so as well.