Well, over the years I have bloomed a few of both.
and hands down, rothschildianum is the EXHIBITION plant. Wow, a good roth can be spotted in a display from 300 feet away. It is a bold flower, great presentation.
Sanderianum is lovely, don't get me wrong, but often it is "looking at the ground" where the dorsal does not stand vertical, rather hoods over, the tawny colors are not as bold as a roth, and transporting a sanderianum in bloom is almost impossible to get it to a show or judging center with the petals intact. David and Justin are right, the flowers without the petals are almost as boring as a randsii. Rare, yes, a bit tougher to grow, yes. But it is not the imposing show peice that a rothschildianum is.
When I stake a rothschildiaum stem for display, the stake only needs to stabilize the presentation, or maybe pull the stem backward a little bit, less than 15 degrees would be typical. Bolt upright presentation is the usual state. A proud flower.
When I stake a sanderianum I have to pull the stem up usually something on the order of 45 degrees. Sandies want to hang their heads, too shy for the exhibit hall. Add the narrow dorsal, etc and you can see why people seem to gravitate toward roths.
If I had to reduce my collection to 5 species, roth would be on the list, not so sure about sanderianum. Micranthum and a purpuratum would make the list.
But since I have the luxury of a little more space than that, I have a dozen mature sanderianum, and 3 mature roths. I have been picking up roth seedlings again. I definitely need more, so I can see one in bloom more often.