I think you should have the best luck not dealing with snow or ice if you take I-5. The main place where bad driving conditions might occur is the Siskiyous which is, basically, at the California/Oregon border.

But your other route might be fine, too. You'll really need to watch the weather forecasts.

4WD can be an advantage in deep snow but really doesn't give you much of an edge in ice. In fact, I see more 4WD vehicles spinning out than other types of vehicles. I believe this is because they have a false sense of security in their 4WD. Planning your trip so you can drive more slowly and safely in bad weather is more important, imho, than 4WD.