Fly Wheel Weight
Flywheel weight helps in smoother pedalling. So, heavier the flywheel smoother is the pedalling.
Type of Bike
Upright Bike - In an upright bike you need to bend the neck and back over the handle just like the traditional bicycle. An upright bike doesn't have any backrest. One can use it in the same way as it would be used in an actual bike. One can even opt for standing up and pedal that way as one can do in a traditional bicycle.
Recumbent Bike - Recumbent bike comes with a backrest and the rider's body can sit comfortably in the bike's frame with the knees almost bent at 90 degrees and your legs to pedal in front instead of down below like in case of the upright bike. Recumbent Bike can be used by elderly people or people with chronic back pain or other lower back issues or even it can be used by the people who want a more comfortable bike riding experience without much intensive workout. Its chair like seat provides an outstanding support to your back, and the reclined position of your body means you may not feel any strain at all.
In an exercise bike with fan resistance, the fan itself is connected to the pedals through a belt & pulley system. So, as you pedal, the fan start to turn, and as your speed increases, so does the air resistance on the blades of the fan. So if you want more resistance you have to pedal fast.
Magnetic bikes has a big advantage because their parts do not wear and tear, as there is no direct friction or even any contact. They use electromagnetic induction in order to provide the resistance to the rotational speed you create by pedalling. Exercise bikes with magnetic braking have a very smooth, continuous resistance, which can be adjusted easily by just the touch of a button.