Would you recomend me which CPU has better performance/price for primecoins mining?
I am using an i7 3770k right now on ypool and make roughly 0.02 BTC per day (and I am GPU mining at the same time). I do not know about the rest of the processors though. If I had to guess, I would suppose that an overclocked i7 3770k is going to be your best bet.