There are pros and cons for each option. If you have enough money to buy a brand new device, then go for it. However, you should also consider the number of times you are going to need the machine. Is it for long-term or short-term use? Will you be able to store them properly and safely while not in use to make sure you keep them in tiptop shape until next use?
You should consider these factors before you make the final decision. If you are on a budget, and will only be using the machines temporarily, and no place to store them, then go for rental rather than buying them.