Gyro or Accelerometer?

I want to make a bubble level with the arduino which component would work better to let me know when the sensor is level and when not and by how much?

accelerometer's measure dynamic acceleration while gyros measure rate of rotation. if your project is static and only rotating then the accelerometer would be the right choice. keep in mind that accelerometers read lots of noise and the usually what people do is buy both sensors and fuse them(in software) to receive more accurate results...