I stacked mine. I would have had them side by side if I had room. I just think (for no particular reason) that stacking them is more dynamic so more movement potential. I have a small Miele set so they are heavy and stable. I have no experience with the larger sets. Mine are stacked using a stacking kit.

Issues? Every one of my front loaders has been in a stacked configuration. I can't say I've ever had a problem because of it. Whatever you do, make sure you still will be able to access the water shutoffs in case of emergency.

Sean_m makes an excellent point. I had the plumber and electrician put all the workings beside my stacked set and then I asked that the carpenter configure the cabinet surround to cover the workings and have full access with the removal of a panel.

Enduring: VERY nice setup on that. Good machines too.

Thanks Sean_m :) I am very happy with the washer. The dryer is a little weak with my "too long" vent run, I miss calculated. I get a fault light related to the vent from time to time. It depends on the fluffiness of the load it seems (?) A few months ago a poster showed me his inline auxiliary fan that he put in with his Miele dryer and it corrected the issue. I have got to do this too. My adjusted run with all the calculated bends is 33'. So the booster fan will be helpful.