Do you want an upright or a recumbent exercise bike? If you have joint or back trouble, the reclined position of a recumbent bike is strongly recommended. Still, many people favor an upright seating position for a number of reasons, including that it more closely mimics the experience of riding a standard bicycle. Both types of stationary cycles deliver the same workout quality.
What are your fitness goals? Chose an exercise bike that will best help you reach your fitness goals. For example, if you need help tracking your intensity and progress, look for a model that tracks distance, speed and calories and contains a built-in heart rate monitor.
What type of resistance do you want? The three primary resistance systems for stationary bikes are magnetic, friction and air, and each has advantages and disadvantages. Magnetic resistance systems are generally the quietest. With air, the bike uses a fan that increases resistance -- and noise -- as you pedal faster. Air resistance bikes require the least maintenance. Friction uses a belt to drive a flywheel. The belt may wear out over time, but this type of bike best simulates the feel of a real road bike.
How much space do you have? Before you purchase something as large as a stationary bike, you should know where you plan to use it. Measure the available space -- length by width by height -- and use it as a reference during your selection. Also factor in the weight of the bike. If it's light enough, you may be able to use the bike in an open space and then move it into storage.