[font color=\'#000000\']I don't know if you're familiar with this territory, but I'll assume it's your first time through. If so, here's what I'd do.
South via Tehachapi and Death Valley over the north route via Reno any day. Tehachapi alone is worth the trip. Love those windmills!
North from Mojave, CA on US 395 gets you to DV via Panamint Valley and Town's Pass, arriving at the dunes. An excellent way to arrive.
Exit DV via CA 190 and DV Junction, stopping at Dante's View just before DVJ.
Take CA 127, CA 178, NV 372, NV 160 to Vegas. Don't laugh. If you haven't seen The Strip in the last three years, you're in for a visual treat. Do it at night, though. Vegas is very busy at Christmas.
Southern UT may be doable, weather dependent.
If the roads are good, I'd overnight in St George, UT and proceed east via UT 59 / UT 389, ALT US 89 to Page, AZ, then south on US 89 to Flagstaff. St George to Page is very scenic, very Utah. You can also keep north on UT 6 though Zion (incredible) and on eastward on US 89 via Mt Carmel Jct, Kanab and Page.
If the weather's iffy, I'd get south, fast. I'd leave I-5 at Tejon Pass, cross the Mojave via Palmdale, Apple Valley, Twentynine Palms and Parker, joining I-10 just west of Yuma and high-tail it across to Tucson.[/font]