Heres my take on the 125vs250 battle,
Are you mature? Both a 125 and a 250 have enough power to get you into trouble, but the 250 will do it faster. Where are you riding the bike? Woods? MX? If MX, both will do fine, but woods, the 250 would be a much better choice for a MATURE rider. If you dont respect the bike, you can get really hurt, and these injuries are giving our sport a bad name. My first bike was a KX125, and I started out riding mostly woods and trails. I loved the bike, and still do, BUT after about 2 months of riding I wish I had bought the RM250 I was planning on buying. I started going to the track after 6 months, and the 125 did great there, but In the woods I wanted the low end of a 250, so I bought a 450 :P