Manual testing versus Automatic testing?

for examples,you selected Spiral Model or Agile methodology as your sdlc, then i would suggest Automated Testing. Because, in these lefecycles, we build the product on incremental basis. While testing Build 2 onwards, the tester has to ensure that previous build's functionalities are fine or not. Here again the tester needs to spend some time to ensure that. But if we do automated testing, while testing build 1 we willbe creating the scripts to test. After receining build, simply execute those scripts, thats it results will be in your hands within minutes.