This is an old thread, however I thought a few remarks might be appropriate for anone else who might make that trip. I have traveled this route probably hundreds of times, and gone across on the other routes as well.
Simply put, use 299. going east, it narrows at Mad River, but widens out for the big climb up to Lord Ellis summit. After topping out, it narrows again and is windy until you get to Willow Creek. The highway joins the Trinity river a few miles east of Willow Creek, and is quite exposed to cliffs between there and Burnt Ranch. In rainy weather this road slides quite often along here. East of there, the river and highway run a little closer together, (that is same level) and the twists ease up some. This is worth just cruising slowly and enjoying the views. Stops are best made when there is a full turn out, ONLY. Loggers still use these roads, and will take risks that will make you cringe.
Eventually Weavervill arises, and worth a stop to view the Museum and Joss House, and walk around the main town, with it;s ornate spiral stair cases. During the gold boom, some buildings had different owners on each floor, so they built stairways to the upper floors. From Weaverville going further east you come to the worst part, Buckhorn Summit. It is steep, narrow, and twisty, with log trucks coming over the line and tight turns near the top.
Very steep going down the east side (or climbing coming from Redding, I come to almost a dead stop at the top, and downshift there, before starting down. Don't wait to downshift until you are going too fast, start slow, stay slow) descending to Whiskeytown lake. Stop to cool brakes, perhaps camp at Oak Bottom. Proceed east to Old Shasta, stop at the museum. From Old Shasta it is still all downhill into Redding, so be careful of your brakes although it is not as steep, it is persistant. Shift down.
299 is surprisingly the best road from Eureka. It passes through some of the most beautiful country in Northern California. Keep your eyes open and you might see a Big Foot.