Myself I prefer I-15, but as has been mentioned, traffic is pretty bad between the Ogden area thru Spanish Fork, about 100 miles of yuk. You'll want to hit it between 9am and 3pm to minimize that. Either route, you often hit temperature inversions, which means a low fog, or haze which coupled with the sun being to the south means you'll probably benefit from good sunglasses.
As for road conditions, it's anyone's guess. We've been getting a fair amount of snow so far this winter, but they've been clearing it up pretty quick.
