Ease of setup and installation factored heavily into our ratings, including whether an account needed to be created and if there were any extra subscription fees necessary. Each unit had cords protruding out of its back, so design wasn't much of a factor in my choice, though parents should take care to keep dangling cords and wires away from their children's reach when setting up a monitor.
It really depends on what you feel most comfortable with. There are audio monitors that allow you to listen to any noise coming from the nursery, vital monitors that track sleep and breathing and video monitors that add sight to sound. Babylist parents overwhelmingly choose video monitors. The security of seeing what your child is up to—like if they’ve gotten tangled in their swaddle, pulled their diaper off or climbed out of the crib—can be worth the extra cost of a video monitor.