at the end of the day you are always going to be at a slight disadvantage against the 250f's but as far as 125's go in standard form the yamahas are as good as they come they arnt quite as fast as the ktm or tm but as an alround package they have it all. my brother had a fully race tuned yz125 that he rode in the dep british two stroke championship last year and that bike would of killed any stock 250f it ran at 39.6 bhp so i would say that they are defently good bikes but if i were you id go for a 250f they dont need tuning to be competetive and the power is more usable and easier to use than a 125's

A friend who is part of the Yamaha Junior Development team where I am has said that the new yz125 is really great and he thinks the new model while not a great deal different from his last one, still improving. Yamaha seem to still be interested in going ahead with the 125cc where Honda has quit on theirs.
If you have to race one against the 4 stroke 250cc class you are still going to be at a disadvantage, but if the class is raced alone with only 125cc the yamaha is a good option.

its' ok,I gess, it's real depend on what you like to ride,and where and how, motocross or freestyel or just fooling arown it all feel's difrent to me, you get on a street bike like a R6 is smoth where's a R1 you barlee tuch in and your up,but it depent's like I said on you ,I go to steet bikes to dert bikes, raceing and then jumps thet are over your head, then four wheeler's and minies for fuom pits,