Range of signal: Some baby monitors have better range than others. If you live in a big house with multiple rooms, range will be a key consideration for you. Anyone who lives in a single-story house or a smaller apartment may not need as much range. Many baby monitors have an alert when you get out of range, and the packaging typically gives you an estimate of the range. Bear in mind that range varies widely from home to home. The construction of the walls between you and the baby monitor may even limit the range.
Many audio/video monitors feature infrared light or "night vision" so you can see your baby on the monitor even when she's sleeping in a dark room. And some audio models feature a night light on the nursery unit that you can activate from the receiver. Other features may include adjustable brightness, and the ability to let you activate music or nature sounds to soothe your little sleeper by remote.
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.