Being that there is a 100mhz clock difference the 3470 will prob be better as its a ivy bridge cpu, but both are a good choice prob very close in performance with the 3470 being very slightly ahead, pick one that u think is in better condition or meets ur price, the 2400 seems the better deal as comparing its retail price to what ur paying for it is alot less than the 3470 retail to asking price. Beside the small gain from SB to IB and 100Mhz on the clock speed both are prob very similar to another in regular everyday use and gaming etc.
that's around 345 euros (i want that the gpu to be new) i could take the 2400 this week, use the intel hd untill i have the money for the gtx. i think i could whait a couple of weeks for that gpu monster )))
i really appreciate your help and thank you very much sir! i can't wait my first power on with this! every year i'm building a new computer as a gift for my birthday )) and that power on is what makes me feel happy thank you again and have a good day !