Machinery 101: You May Want To Read This Before Hiring an Excavator
They are not all the same
As with any other heavy construction equipment, excavators are not a 'one size fits all' kind of equipment. The kind of work you want to do will determine what kind of excavator you should hire.
Now, as a side note, excavator hire is nearly always better than buying, especially for the really heavy equipment. Unless you are starting some kind of construction company that will have you using these kinds of equipment often, hiring is more affordable and less involved than purchasing.