Effectiveness can be measured based on the fields out here, it totally relies on what type of criteria are you looking for. I would say neither of them is better. Here are few measures that will definitely answers your question: 1. Ability of the person who is testing the application whether it is being tested manually or by automation. 2. The type of application which is being tested. Sometimes automation testing is effective and sometimes manual. 3. The test strategy, tools and techniques being using for testing. If these three terms are well defined then both manual and automation can be effective. 4. Cost of testing. The most importantly cost of testing an application specifies which one would be better. 5. In terms of career in software testing field, both will be having their own effectiveness based on the requirements.