in 20 years of writing SQL, preceding commas is so much better IMO. Its so easy to miss a comma at the end of a long expression. preceding commas means you can never forget them.

Then if I can have an extra leading comma, I can reorder, comment out or remove, or add a column at any point in the list without having to think about the rest of the projection. Also diffs are cleaner, it only highlights the rows that have changed, not the row above it/below it that had its comma added or removed. This happens a ton when im iterating on a query.