Ia! Ia! Cthulhu ftagn!
Doesn't matter much to me, since I'm not buying into 4E. But I do prefer the 1-square-is-1-square method. It's just simplest and comes the most naturally; people are less likely to mess up when figuring out their movement, they'll get it figured out quicker, and I as DM don't have to manually calculate
every dang critter's and PC's movement in exacting detail to be sure that it was right. So combat runs quicker and more smoothly.
And I handle the firecube problem by just ignoring WotC's silly wrong concept of how spell areas should be based on grid corners and how every square is affected if even just a little bit of the spell's area passes through the edge of the square. I use simple common sense to figure it out and not WotC's funny version of mathematics.
I'm all for abstraction in D&D, but not for throwing semi-realism completely out the window. It's not hard to ignore a minor oddity in diagonal movement, but it's more unusual to think of fireballs and cones of cold and other things behaving like massive collections of cubes. And similarly frustrating for WotC to treat every creature and object as though it has the body type and proportions of a Gelatinous Cube.