Do not buy generic motorcycles. When one needs repairing, it's hard to find a mechanic to fix it. My brother owns a generic 110CC motorcycle. After he rode it for two months, the muffler burned out and now it needs a new one.
Mufflers won't burn out on name brand motorcycles and if they do, it takes a long time to happen.
A name brand motorcyle is sitting on a balanced frame. A generic is not. This makes generic motorcycles more difficult to ride.
Yes generic motorcycles are cheaper. But you'd be better off buying a used name brand than a brand new generic.
The name brand motorcycles are: Honda, Kawasaki, Suzuki, and Yamaha. I give Generic motorbikes a 3 star rating.

In descending order of value for money:

HONDA
BMW
YAMAHA
SUZUKI
TRIUMPH
KAWASAKI
DUCATI
HARLEY DAVIDSON
VICTOR
BUELL

I'd suggest staying away from off-brand bikes, as they could be dangerous and unreliable.