Yah, that was the opinion of many. Even members of the Zill family prefer LZ. And, I was told that LZ won the taste test a couple of years back.
The OS is a 'commercial' quality mango; I was told that it was selected for its suitability to be marketed on a commercial scale. For one, it has a better shape for packing/shipping. Secondly, it is slightly more productive. Most of us realize the difference between the fruit and veggies we find in the supermarket vs what we can grow in our backyards. The OS is a commercial fruit where the LZ is a homeowner fruit.
I know one individual who is topworking his OS tree to LZ, if that gives you any indication as to the quality difference :-).
The LZ is a definite winner in my book. I've had LZ fruits from both Walter's tree in Delray and a tree here in Broward. The tree in Broward produced more consistently excellent tasting fruits, where Walter's tree seemed to produce some blander fruits and some excellent fruits. So, those of you who've tried 1 or 2 LZ fruits from Walter's tree should really wait before finalizing your opinions. Walter's wife rates it as her #1 favorite mango of the umpteen cultivars she's gobbled own in the past couple of decades.