We like the Micro scooters, ds1 has had one since he was about 4, and we are buying one for ds2 for his 4th birthday as well. All the other scooters they have had seem to fall apart pretty quickly.
Ds1 has a Micro Sprite but the handles are actually a bit high for him if we have it on one of the pre-set heights, so it might be a bit big for your 3.7yo.
We have bought a Micro Lite for ds2. Loads of people round us have their kids on Mini Micros (with two wheels at the front) but what puts me off is that they are heavier at the front so it's quite easy for the kids to fall over the handlebars.
www.micro-scooters.co.uk/index.php