If preserving the wood is the most important thing to you, then the safest way would be using a regular mop and microfiber dust mop. Firstly, wash the floor with a very light cleaning solution and then use the microfiber dust mop. But this an ideal option.
Of course, I understand that nobody in the world has this much time to waste on the floor, so any of the steam floor cleaners set to the lowest output will do. I prefer the floor cleaners with spinning mop heads for hardwoods, because I can control the water and cleaning solution output.