Well, Sound Lab is very good anywhere basically. The 45 degree dispersion is well controlled so you have very few wall reflections even in a narrow room (and toe-in a bit makes sure of that too)
If you had to choose which room to put Sound Lab, you may enjoy the listening and sound from a larger room with the SL having more space and you could think of getting the 7 cell (widest) versions which have the benefit of slightly better lower frequency response. (wider panels reduces bass cancellation but they all sound excellent) If you were to think of the narrow room, then a more narrow SL would fit better (visually) and because they are tall will certainly sound better than the shorter Quad (in my opinion) – you may start with one (for whichever room) and I suspect you might fall in love with them and want for both rooms 🙂