What would be the best chemical elements for a shapeshifter to turn into?

If someone had the ability to shapeshift into any chemical element, compound, form or material while still maintaining normal human speed/motion like Metamorpho and Absorbing Man what would be the best and most versatile elements to turn into for combat, surveillance, evasion, crime fighting etc?

This is why real world phycics, chemistry, and biology should be refrained from battle board discussions. For example, what happens when you vigorously bend a metal hanger back and forth? Friction? Anyway real world sciences are often ignored for story.