Running on a treadmill and indoor cycling each have their own advantages. Before choosing one over the other, consider your budget, training goals, and physical ability.
The quality of the workout depends on the intention and intensity of the user. Both of these kinds of equipment can offer a great workout and help you burn lots of calories.
Spinning is much easier on the joints. Running creates more impact than spinning and may not be the best option for those who deal with joint pain. That said, spinning can harm your posture, and those who sit at a desk all day may want to be upright during their workouts.
In the end, neither is necessarily better. Both activities offer a great workout that can be done at home. The choice comes down to the needs of the user and personal preference.