I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "Many types of Turing machines are used to define complexity classes, such as deterministic Turing machines, probabilistic Turing machines, non-deterministic Turing machines, quantum Turing machines, symmetric Turing machines and alternating Turing machines. They are all equally powerful in principle, but when resources (such as time or space) are bounded, some of these may be more powerful than others."? 

What is important when deciding which Turing machine to use?