On I-5 the commercial traffic is all long haul with few on/off ramps. Hwy 99 has many towns with many on/off for all of the short haul business, produce and delivery traffic. Take your pick. Also I-5 is all 2 lane in each direction while 99 varies between 2 and 3 lanes here and there without reason as it does not seem to always be near towns. There are sections of I-5 where the right lane flat beats you up and chatters your teeth for miles with a beat up surface. Last month there were some sections on south I-5 where lanes were split for as much as 5 miles at a time. One lane on the old roadbed and the other 100 feet to the left on some north bound roadway. Nothing like lots of close cement K rails to stay between. But the locations are always changing so where they are today I do not know. Flip a coin and enjoy the ride.