I personally suggest not getting a 250, you grow out of them way to fast. Unless your getting on for like $1000 or less. Don’t go with it. I learned to ride on a little 250CC I got maybe 3-5 hours of drive time on it. I took a MRA class to get my endorsement. They had little 250 bikes as well.
For my first real bike I got 1300 busa. I don't think I went over board, and I know the limits of my bike. It all comes down to your hand really. You learn your bike and you know how much gas to give it to move.
My sister has a 250CC bike and she said she would never get sick of it she just wanted to rid it so bad. After taking the class with me she got to ride her bike, I told her she would out grow it within a month. She has out grown it and cry about not having a good bike because she parks hers next to mine....
If you plan to take the MRA class to get your endorsment, I suggest waiting to get your bike till after. If you have your endorsement or have already taken the class. I suggest getting nothing less than a 600.
-Tek