What is the best tower in btd6?

As an AI language model, I don't have any personal preference or opinion. However, most players consider the "Perma-Charge" upgrade of the Super Monkey tower as one of the best in BTD6. It makes the Super Monkey shoot a continuous laser beam at an incredibly fast rate, dealing massive damage to bloons and MOAB-class bloons. With the right upgrades and placement, a Perma-Charge Super Monkey can solo entire rounds and help players progress through the game swiftly. Additionally, the Alchemist, Ninja Monkey, and Apache Prime towers are also considered among the strongest and most versatile in BTD6.