Software teams are under constant pressure to release faster without letting quality slip, and one of the most consequential decisions they make is how to split their testing effort between manual and automated methods. The debate is often framed as a choice between the two, with advocates of automation promising speed and repeatability and advocates of manual testing pointing to human judgment and flexibility. This paper offers a structured comparison and a practical method for optimizing the mix. We map testing activities to the phases of the V-model of system development, analyze the economics of automation through a cumulative cost model that shows an initial investment followed by a break-even point and then cumulative savings, and compare the two approaches on defect detection, cost, speed, maintenance burden and coverage. The comparison is based on a study of four industrial systems, a web store, a mobile banking application, embedded device software and an enterprise resource planning module, observed over 24 release cycles. Automation broke even after 4.5 to 12 release cycles, depending on the system, and reduced regression testing effort by 37% to 68% after 24 cycles. Automated tests were first to find 65% of the 1,046 defects recorded, dominated by regression, integration, performance and compatibility defects, whereas manual testing found 88% of usability defects and 79% of exploratory logic defects. A risk-based hybrid reduced total testing cost by 39% against an all-manual approach, lowered escaped defects from 7.8 to 3.4 per release and raised requirements coverage from 71% to 91%, while automating everything saved only 16% and let more defects escape. The paper concludes with a decision guide for allocating test effort.