If you're traveling in December the most direct route (over Tioga Pass near Yosemite) is going to be closed by snow -- its closed all winter for that. So your only two routes are north to Reno/ Tahoe and west over Donner to Sacramento and beyond, or south around the Sierras and west to Bakersfield and then up through the Central Valley. Both are 2 day trips, although the southerly route is slightly faster.
For scenery, the Tahoe/ Reno route is much more scenic -- you'll go up the eastern side of the Sierras and pass by the major ski resort of Mammoth Lakes (lots of snow-capped mountains, and perhaps some along the road), and Tahoe is gorgeous in the winter. The other route will take through the high desert to the Central Valley of california, which is a huge agricultural area with numerous orchards, fields and towns. Some nice places to stop for agricultural products, wine tasting and the like -- but not as scenic.