Slide that is weighted to close on it's own. This way, you can prop it open if you wish, but in inclement weather, it closes when you let go of it, freeing you to attend to the order faster.
RedBaron, did you make a decision and find a window?
I am looking for a smaller slider. Have had a hard time finding one that is small enough in outside dimension, as well as thin enough in the depth of its casing to install in a regular exterior door.