Both are bad choices.
Motorcycles are like airplanes and the faster ones kill their pilots faster. When I hear about stupid ideas like this, I am reminded of an airplane that people used to call the "Doctor killer".
Race bike present challenges that a new rider is better served by learning on more forgiving rides, such as the Shadow VLX, the Rebel and the other 400cc - 600cc cruisers. Once you have the practical experience (all weather and all configurations) and proper training, then move to the race bikes, if you still want to. But once you have the experience, you will find that the 250's might be less than you want.