What appears to be the fastest driving route between Salt Lake City and Denver?

Answer 1

On a map, just eyeballing it, US-40 looks fastest, because it is the shortest (488 miles), but it is actually the slowest, probably because it is a smaller road and the speed limits are lower.

I-25 to I-80 (522 miles) is technically the fastest (through Wyoming), but only by about 15 minutes, and the I-70 route (525 miles, over the mountains) is the best choice because it is fast AND has amazing scenery, which you are not going to get in Wyoming.

I-80 is best in extreme bad weather though, because the pass could shut down, and then you couldn't get over the mountain (or they sometimes require chains)... but thankfully that doesn't happen often.