If you are a Spark shop then choosing Delta over Iceberg is a no-brainer. It's simpler and perfectly integrated. Not to mention that the Spark's Delta connector can now generate Iceberg-compatible metadata too.

The choice between the two resembles the choice between Parquet and ORC circa 2016. Two formats of broadly the same power, initially biased by a particular query engine, eventually at feature parity and universally supported.

We have got a decade of experience with OSS from Databricks so doubting their "open ecosystem" status seems a little theoretical.