def the K for sure, b series all have v-tec kickin in around 4-5k rpm's and the great thing about K's are that they have i-vtec which will kick in at any rmp range, also the fuel system is much better, and the computers are a bit better due to better technology and they can dump more fuel in than the b series bc of that simple fact, which means less engine bog when youre launching at a track if you dont have an upgraded clutch...plus just in displacement the K's are larger which means they have a higher capacity to make whp.