Ebony was the original Singita lodge and so styled more in the traditional Colonial style. It underwent a total renovation a year or so ago and is truly superb. Boulders underwent a renovation about two or three years ago. It is more contemporary in style but still very organic. The accommodations are breathtaking in both lodges with private plunge pools, your own butler, great food and service. Personally, I prefer Boulders but that's just me. Others prefer Ebony. You can't go wrong with either. Be sure and reserve far in advance because there are very few accommodations in either and they fill up fast.
As for Londolozi it's a wonderful property too, especially Tree Camp or Granite Lodge. If you can't get in to Singita it's a viable option.
Also check out Royal Malewane, another one of my favorites.