Best hard surface floor cleaner

Answer:  I haven't found one that's worth paying for.  Not a consumer-grade appliance, at least.  There may be professional equipment for sale out there that works, but that's not practical for a single family home. 

This is not a rigorous scientific study, but here are my latest test results:

On the right:  The mop pad removed from the most recent device I brought home from the store to try.  This photo shows the results after the device had "steam cleaned" approximately 100 square feet of ceramic tile in my kitchen.  A light coating of dirt is visible on the pad.
On the left:  A damp wash cloth that I then rubbed over approximately 16 square feet of the same floor area that I had just cleaned with the steam mop.

In other words, the hand print indicates the degree of dirt that the mop left behind in a small subset of the "cleaned" area.  I estimate that the fancy steam mop picked up about 10% of the total dirt on the floor.  The rest it just spread around, causing visible streaks.  The floor looked worse after steaming than it did before. 

And I did RTFM on this one.  I followed the manufacturer's directions carefully.

We have no wall-to-wall carpet.  Our entire house, all 2,500 square feet, is finished in ceramic tile, which I describe in this post.  I intentionally chose a tile with a smooth matte surface so that dirt would not stick to it. 

Here's a low-light photo showing the surface.  It's textured enough to be fairly non-slip, but not textured to the point where there are grooves and ridges that trap dirt. 

And it has, indeed, been an exceptionally low-maintenance floor to the point where most of the cleaning is taken care of using this robot vacuum.  But everything needs to be washed once in a while, and I would be willing to pay for a mop appliance that can help with that task, given that (a) I have so much square footage and (b) it's not heavily soiled, so even a mediocre appliance should be expected to pick up what limited dirt is usually present.  So I've recently been trying out different models because it seems to me like real advances in technology should rightfully have occurred by now.  Advances have certainly been realized for the cleaning of clothing - why not floors??  But I've been cleaning hard-surface floors the exact same way for more than forty years now - with my hands and with a conventional cotton wring mop.  Alas, it looks like I'll be continuing that way for a while longer, because none of the products I've tried actually got the job done.

But there's a silver lining to all of this.  Properly approached, a hand-done floor wash can provide a good yoga-style work-out, combining elements of Plank, Down Dog, Cat-and-Cow, as many Sun Salutations you want to add as you jump up repeatedly to rinse your cleaning cloths.  Unless you have physical disabilities that restrict your movement, the old way is certainly better for your health and it's absolutely better for your pocketbook, as many of those fairly useless steam mop gizmos cost one to two hundred dollars apiece (!!). 

Happy scrubbing!!

Picture this dude wearing rubber gloves and with a cleaning cloth in each hand. 

Image screengrabbed from this "Yoga For Healthy Aging" BlogSpot post.