I'd definitely keep it out of the corners - that's one setup that always drives me nuckin futz.
The corner overflows have always boggled my mind, why people always choose them is beyond me - it's relatively rare that a tank is only viewed from the front - making that choice rather odd. Suppose it's probably cheaper (1-2 less pieces of glass), and that could explain a lot.
You've probably already chosen your equipment, so sit down with a pad, figure out what will fit best where, and where the overflows would be least obtrusive. There's any number of possibilities, but try to make the overflows work best for you - no point having to work around them at this stage.
Some reading on the planted tank forums about "The golden rule" and other basic aquascaping principles. They can give you some valuable insight about rock placement/layout and what will look good with the choices you do end up making.
Andy