what bike should i get a 04 kx125 or a 04 cr125.?

Out of the two you mention the cr125cc would be the better option. The kx's have improved greatly over the last few years but I don't think all that much of the 04 model. But then in saying that if you can pick up a kx125cc that is in excellent condition then you should go for it. The condition of the bike should play a bigger part in your decision on which to purchase.

If you were buying new I would suggest the yz125cc as they are the better bike in a 2009 model, but since you are not just focus on getting the best price and the bike in the best condition, that has been well maintained. Get someone with experience to check the bike over before you purchase as you don't want to waste money on a lemon

You should get a 04 yz 125....