The evolution of big data architectures from static warehouses to dynamic lakehouses has driven demand for storage formats that balance high performance, scalability, and strong data reliability. This paper provides an in-depth comparative study of Delta Lake and Apache Parquet within Python-based data pipelines, exploring their architectural differences, performance benchmarks, and operational implications. Using simulated workloads and a review of peer-reviewed literature, the study evaluates read/write throughput, concurrency, schema evolution, governance, and total cost of ownership. Results demonstrate that Parquet remains highly efficient for stable, append-only analytical workloads, while Delta Lake extends functionality with ACID transactions, schema evolution, and time travel, improving reliability and flexibility for mixed batch-streaming environments. The findings inform practitioners designing modern data lakehouse systems that integrate analytical and operational workloads under unified governance frameworks.