Mine are side by side and I use the tops for folding clothes since I have no other place in the laundry room to fold.

Mine are side by side too, and I do lots of stuff on the flat tops. My washer and dryer are stackable, but I prefer them side by side.

Side by side because there's plenty of room.

What's nice about side by side on a front loader is you can get the pedestal to raise them.

But if you get the pedestals, you can't use the top surface.

Mine are stacked because I also keep an upright freezer in the laundry area, and there is no folding space there. My remodel will either keep them stacked with a counter next to it for folding and storage, or appliances under the counter.

I've had them both stacked, and on pedestals side by side. I feel the pedestals are a waste of space and money, and prefer stacked.

I have both stacked set up on the main floor and unstacked in the basement. The basement is rock solid because of the concrete. The main floor set will show a little jiggle for the dryer when the washer is kicking into a high gear spin. They are very level, but the floor is a wood joist floor. It is somewhat reinforced with blocking, and it is in a corner where 2 load bearing walls meet.

Side by side. I'm 5'1"--and a stacked full-size dryer would be hard for me to reach. This may not apply to you :-), but even if you're taller, do you have kids who you want to start doing their laundry?

If you have the room go with the side by side arrangement. If your washer and dryer are stacked and the washer needs to be serviced the company will likely have to send out two repair techs rather than just one. The second tech is needed to take the dryer off of the washer so that they can get access to the insides of the washer. This could lead to a higher repair bill.