Standard stationary bikes provide you with a workout that is good for your quadriceps.
Recumbents provide all the benefits of regular bikes, plus they work the gluteal and hamstring muscles more than traditional bikes.
IMO bikes would help you keep strength and leg muscle size over walking because it will " shock" your muscles. The average person walks 6000 steps a day so riding the bike will provide a different strain on the muscle and uses a different range of motion.