It depends.

If the cabinets are captured between two walls (where you cannot see the sides of the cabinets), deeper cabinets--18"--are great.

OTOH, if the cabinet sides are exposed, IMO, deeper cabinets will look too heavy and would bug the heck out of me. IOW's, a case where form wins out over function.

The cabinets would be captured between two walls.

Thanks

IKea makes 15" deep upper cabinets. I would be careful of the depth, because they will be hard to reach into. I had uppers above my sink and toilet in my old bathroom before I remodeled it. I called them "hell holes" because I think they might have been 24" deep. Lots of crap got shoved in there and impossible to retrieve.

Then definitely go for deeper cabinets.

Last house, I had cabs captured between two walls and over the W & D. Site built cabinets/ old school. Cabinets were the standard depth--the width of a 1 x 12. I removed the doors, popped the face frame off and added a 1 x 6 to make wider shelves. Re-installed the face frame and doors. Was easy & inexpensive way to gain 50% more storage space.

If budget permits, deep cabinets with roll-outs (like a pantry) will help you utilize the rear space. A lot of folks put these over their refrigerators nowadays.

one of the concerns we have is hitting our heads on the cabinets when we are removing the clothes from the top load washer

Gle, I never banged my head on the cabinets that I extended (with a top loader installed.)

To alleviate your worry, you could try mocking up a shelf or just stretching a string between the walls (or one of those torsion spring shower curtain rods) at the point when the front edge of the cabinets would project to. As I said, was not a problem for me but might be if you're tall. (I'm 5'5".)

Enduring makes a good point about things getting lost in the back of deep cabinets. That wasn't a problem for me because I used the storage for my canning supplies--water bath canner/ pressure cooker/ canning jars, back up inventory of powdered detergent bought on sale, etc. I.e., bulky items. (House was on a slab with no basement so I had to maximize storage where ever I could.) So know what you plan to store there before going to added expense of deeper cabinets.

Items are generally easier to retrieve on the lower shelves because they're closer to you. My cabinets extended to the ceiling; anything on the upper shelves, you would likely need a step ladder anyway. I was younger, thinner then, so I just hoisted myself up onto the top of the washer and pulled whatever off the top shelves.)

The downside to deeper cabinets (or any cabinets, for that matter) hanging above the W/D is that it's more difficult to do the install--hook up the dryer vent, water & drain connections. (Generally helps to install dryer first.)