Why would you want to use a steam cleaner on a painted wall? I guess it would depend on what the wall is made of and what type of paint. Flat latex paint on drywall - I would pass on the steamer and instead spot clean with a moist microfiber cloth.

Better at getting out stains from carpet and grout? Any of the good units will do fine - it is the technique of the operator that will make the difference.

It is difficult to compare the machines because the information depends on how the company chooses to present it. From what I read, are that you want a stainless steel boiler and a long enough cord for convenience. Then you want to compare temperatures in the boiler and at the tip. The warranty should tell you something about the machine as well.

I wish that Consumer Reports would test them.