The answer to 'which is better variable speed or single speed AC' is that variable speed air conditioners are generally better than single speed models. Variable speed ACs can adjust their output to match the cooling needs of your home, providing more precise temperature control, better energy efficiency, and quieter operation.
Variable speed systems use an inverter-driven compressor that can adjust its speed to only provide the exact amount of cooling needed at any given time. This allows them to run at lower speeds most of the time, using less electricity and reducing wear and tear on the components. Single speed ACs run at full blast whenever they're on, which is less efficient and can cause temperature swings in your home.