Before buying Samsung or LG make sure there is authorized repair service in your area, service is sketchy for both brands. Not sure but I think if you stack there is less of a vibration issue, at least I have not heard of an vibration with any stack set. Just one thing to keep in mind buying front load washer and dryer and stacking them. If you do need service the tech would most likely NOT unstack if needed.

regardless of which machine you by you should reinforce your floor in the laundry room by decking it with 3/4 plywood where the product sits.

Electrolux at one time had a second floor guarantee or something like that. I guess it still applies to current models.

Our Electrolux would be fine on second floor.