All. But mostly open. If the ball is coming right towards you you can step into it and finish OTS. However for most shots you want to step out - swing more across the body and finish lower with a WW swing. If you watch the players on the tour they are mostly doing this..
Actually very occasionally they will used closed stance too. In squash you frequently hit out of a closed stance but of course its a backspin/flatish sort of squash shot. Pros will use this as a 'emergency' measure. But in truth they can hit it pretty reliably. You can use this shot on both wings - but I am not certain its something a rec player needs to practice.