None, they all suck.
im not sure about that but i can say that a 2 stroke 125cc is faster than a 125cc 4 stroke and probably 200cc too. a 125cc 2 stroke would throw you off the back if you cant handle it properly, where as the 4 stroke wouldn't scare the living daylights out of you
for a 4 stroke: beginner level 2 stroke: experienced they are huge
RX 2-stroke
Kawasaki is the best 125cc dirt bike. Hopefully this link will helps you.
A KTM 250sx is the worlds fastest 250 2 stroke dirtbike.
The size or displacement of the engine, 50cc versus 125cc.
there are no age limits for dirt bike. but there are recomendations for size
it is 33.1 in
It's a dirt bike that uses a 2-stroke engine.
you would need about a 125cc 2 stroke
Depends on the kids experience with bikes. And I assume your talking a dirt bike. If he has no experience I would say a 100-125cc 4 stroke. Personally I would get a 4 stroke bike such as the newer Honda models.