Vented or Condensing? Condensing would be more convenient (vented would mean dropping the vent out of a window as we're in a flat), but I've had horrible experiences with condensors - my mum's Bosch has some kind of filter that needs to stripped and cleaned every month or so and it takes over an hour to dry a single shirt, whilst making the room it's in clammy. Are there any problems that can arise from having a tumble drier go up to get out of a window (condensation trickling back down perhaps?).
Less electricity used is nice, but I also want to be able to put the washer on overnight, get up in the morning and chuck clothes (ie, a shirt or a pair of trousers) into it for an hour and have them dry to go to work in.