At the end of the day, it boils down to "cost" and "preference." Like aTE, I like to buy the "best technology" I can afford, so if I was in the market for a new mower, then I would probably buy the newest steel deck mower. On the other hand, some people might not want to invest in the "newest" technology and go with the current models (20" or 21"). Either choice will work fine, it's really up to you and what your budget can bear. Good luck with your final decision and let us know which model you choose ... :-)
Brushless motors are typically 85-90% efficient whereas brushed DC motors are around 75-80% efficient. This difference in efficiency means that more of the total power used by the motor is being turned into rotational force and less is being lost as heat.
Brushed motor Advantages:
Simplified wiring: Brush motors can be wired directly to DC power and control can be a simple as a switch.
Brushed Motor Disadvantages:
Electrically noisy: The switching action of the commutators constantly creating and breaking inductive circuits creates a great deal of electrical and electromagnetic noise.
Brushless Motor Advantages:
Long lifespan: No brushes to wear out
low maintenance: No brushes to replace
Brushless Motor disadvantages:
High initial cost: Need for commutating device like an encoder and a drive or controller