Proper shutter speed for fireworks?

Hey everyone. What are your thoughts on shutter speed for fireworks?

This weekend, @chicagophotogirl went to a fireworks show and, of course, we both brought cameras. I brought my trusty Panasonic FZ50 and she brought her Sony a6000. Like always, we immediately got into a photography related debate... which shutter speed to use. My stance was 2 seconds... @chicagophotogirl claims 30 seconds is ideal.

What shutter speed do you use?

A few samples of mine using the 2 second speed:

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