Mormon Emigrant Trail / 88 is by far the more scenic route, and the way I'd go. See also http://www.chainreaction.com/emigranttrail.htm

Mormon Emigrant isn't plowed, so it stays closed until the snow melts. It was still closed on July 2nd this year (when I'd planned to ride it last), and I'm not sure when it finally opened. The fall colors along 88 make this time of year the perfect time to ride it.