At least for the fermions the answer is a nice power of two for each generation. There is the electron, the neutrino, the red, green and blue up quark and the red, green and blue down quark, giving 8 fermions per generation. Since one can distinguish between particles and antiparticles, one could also argue for 16 fermions per generation. Also one can distinguish between left and right handed particles, giving a total of 32 fermions per generation.