See this M.Y. question for a brief description of "upper" vs. "lower" trope for the 10 Commandments.
Most Nusach Ashkenaz shuls that I have attended use the upper trope while reading the 10 Commandments. The 10 Commandments are read 3 times during the year:
- Shabbat weekly reading of Yitro
- 1st day of Shavu'ot
- Shabbat weekly reading of Va'etchanan
On all 3 occasions, I have heard it read using the "upper" trope.
Are there any communities / nuscha'ot exiting today, that read it using the "lower" trope version, as part of one of the above readings? Do they do this throughout the year or switch it for one of the 3 above occasions? If you know why they do this, (i.e. - lower always or switching), please add this info to your answer.
Are there any halachic opinions that state a preference and / or time to use one version vs. the other?