The biggest I ever operated was a 5.5t excavator and for me even a small excavator like that was one of the most impressive human creations I ever used. The power is simply unbelievable compared to human strength. You move masses of soil in seconds which would take days with shovels. You can rip out trees and move huge rocks like nothing. And it's so freaking easy to get a feeling for those machines. After a few minutes the excavator feels like a part of yourself.