If you are going to bakersfield, the 99 would be quicker, but if you get stuck anywhere along the way, you are STUCK.
Fresno, stockton, modesto, the prior post about turning into a homebum isint bullshit, those pplaces wont let you leave, at least on the 5 there are places with good on ramps and smaller towns.
People on the 5 are traveling a longer distance, and there is moe local traffic on the 99, also alot of agriculture traffic on the 99.
You could always goo to stockton and try to get a train going south, BNSF takes you directly to bakersfield (GM only)
If you do fly a sign on the 99, id definitely make is say "Bakersfield" and not "South"