Balance bike has more benefits. At 20 months old, its also about motor skills and gross skills. With a balance bike, they can grow with it. It is also safer then a scooter. I never liked a scooter myself. Id stick with the balance bike, and upgrade to a bicycle later on.
Balance bike is more value for money. Can transition to pedal bikes in future. Scooter more for play
balance bike will be better and more worthwhile!