Ohhh, you might as well ask which is better- Coke or Pepsi.
Manual awnings are stronger but more work setting up and taking down. There is more flexibility with manual awnings in adjusting pitch on them for cleaning and sun/shade making.
Power awnings arms are way weaker, but they're just a push button to setup/take down. Many with power awnings use support poles to give them the same strength as manual awnings.