I swap back and forth between a 16" wheel Piaggio Liberty 150i and a 12" wheel LIKE200i - and the difference is quite noticeable.
In the 150 class of step through scooters, the 12" wheels just can't compare with a big wheel scooter!
The ride over city streets is better, and once out on a country road big wheels are even more impressive!
Big wheels equal smoother ride in town and much more stability on the open road.
When I'm 'cruising' a country road - I look down and see that I am traveling about 5mph faster on the Liberty, than on the LIKE....and it has nothing to do with engine size or suspension.
Anyway - if you're in the market for a 150cc class scooter, I urge you to give a big wheel scooter a try before you settle on a 12" wheel!
I've no statistics - but I think the Europeans choose to ride mostly big wheel scooters.
Stig