It's impossible to definitively say which volcanoes are the "worst" as there are different criteria to consider and the impact of a volcano depends heavily on its location and the circumstances surrounding its eruption. However, here are three volcanoes that are often cited for their devastating historical eruptions:

1. Mount Vesuvius (Italy): Known for its 79 AD eruption which buried the Roman cities of Pompeii and Herculaneum, killing thousands. Its eruptions have been responsible for significant destruction and loss of life throughout history.

2. Mount Tambora (Indonesia): This volcano's 1815 eruption is considered the most powerful in recorded history. It caused a global "year without a summer" with widespread crop failures and famine. The eruption resulted in over 90,000 deaths.

3. Krakatoa (Indonesia): The 1883 eruption of Krakatoa was incredibly violent, generating tsunamis that killed over 36,000 people. The sound of the explosion was heard thousands of miles away, and the volcanic ash significantly impacted global weather patterns.

It's important to remember that other volcanoes, such as Mount St. Helens (USA) and Mount Pinatubo (Philippines), have also caused significant destruction and loss of life. The impact of a volcano is a complex combination of factors, and these are just a few examples of those that have been particularly devastating.